BUG: Exception while loading XML with XPath
### 

- [X] I have checked that this issue has not already been reported.

- [X] I have confirmed this bug exists on the [latest version](https://pandas.pydata.org/docs/whatsnew/index.html) of pandas.

- [ ] I have confirmed this bug exists on the master branch of pandas.


### Reproducible Example

```python
import pandas as pd

xml = '''<RootNode>
  <Child1>Text1</Child1>
  <Child2>Text2</Child2>
  <Node1 name="Child3" value="Text3" />
  <Node2 customname="Child4" some-attr="blah blah" value="Text4" />
</RootNode>'''
xpath = ".//Child1/text() | .//Child2/text() | " \
        ".//Node1[@name='Child3']/@value | " \
        ".//Node2[@customname='Child4']/@value"

df = pd.read_xml(xml, xpath=xpath)
```


### Issue Description

Last line `pd.read_xml()` throws next exception:
```
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "C:\Users\[USER]\AppData\Roaming\Python\Python39\site-packages\pandas\io\xml.py", line 927, in read_xml
    return _parse(
  File "C:\Users\[USER]\AppData\Roaming\Python\Python39\site-packages\pandas\io\xml.py", line 728, in _parse
    data_dicts = p.parse_data()
  File "C:\Users\[USER]\AppData\Roaming\Python\Python39\site-packages\pandas\io\xml.py", line 400, in parse_data
    return self._parse_nodes()
  File "C:\Users\[USER]\AppData\Roaming\Python\Python39\site-packages\pandas\io\xml.py", line 455, in _parse_nodes
    dicts = [
  File "C:\Users\[USER]\AppData\Roaming\Python\Python39\site-packages\pandas\io\xml.py", line 457, in <listcomp>
    **el.attrib,
AttributeError: 'lxml.etree._ElementUnicodeResult' object has no attribute 'attrib'
```
Same XPath expression works in `lxml` which is used as default xml parser. For some reasons `pandas` fails to get attribute value `/@value`, if I remove this from expression it doesn't throw any exceptions.

With simpler XPath (`.//Node1[@name='Child3']/@value`) it throws another exception:
```
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "C:\Users\[USER]\AppData\Roaming\Python\Python39\site-packages\pandas\io\xml.py", line 927, in read_xml
    return _parse(
  File "C:\Users\[USER]\AppData\Roaming\Python\Python39\site-packages\pandas\io\xml.py", line 728, in _parse
    data_dicts = p.parse_data()
  File "C:\Users\[USER]\AppData\Roaming\Python\Python39\site-packages\pandas\io\xml.py", line 397, in parse_data
    self._validate_path()
  File "C:\Users\[USER]\AppData\Roaming\Python\Python39\site-packages\pandas\io\xml.py", line 505, in _validate_path
    raise ValueError(msg)
ValueError: xpath does not return any nodes. Be sure row level nodes are in xpath. If document uses namespaces denoted with xmlns, be sure to define namespaces and use them in xpath.
```
### Expected Behavior

```python
from lxml import etree

xml = '''<RootNode>
  <Child1>Text1</Child1>
  <Child2>Text2</Child2>
  <Node1 name="Child3" value="Text3" />
  <Node2 customname="Child4" some-attr="blah blah" value="Text4" />
</RootNode>'''
xpath = ".//Child1/text() | .//Child2/text() | " \
        ".//Node1[@name='Child3']/@value | " \
        ".//Node2[@customname='Child4']/@value"

root = etree.fromstring(xml)
result = root.xpath(xpath)
# returns ['Text1', 'Text2', 'Text3', 'Text4']
```

### Installed Versions

```
INSTALLED VERSIONS
------------------
commit           : 945c9ed766a61c7d2c0a7cbb251b6edebf9cb7d5
python           : 3.9.7.final.0
python-bits      : 64
OS               : Windows
OS-release       : 10
Version          : 10.0.19043
machine          : AMD64
processor        : AMD64 Family 18 Model 1 Stepping 0, AuthenticAMD
byteorder        : little
LC_ALL           : None
LANG             : None
LOCALE           : 
pandas           : 1.3.4
numpy            : 1.21.4
pytz             : 2021.3
dateutil         : 2.8.2
pip              : 21.2.3
setuptools       : 57.4.0
Cython           : None
pytest           : None
hypothesis       : None
sphinx           : None
blosc            : None
feather          : None
xlsxwriter       : None
lxml.etree       : 4.6.3
html5lib         : None
pymysql          : None
psycopg2         : None
jinja2           : None
IPython          : None
pandas_datareader: None
bs4              : None
bottleneck       : None
fsspec           : None
fastparquet      : None
gcsfs            : None
matplotlib       : None
numexpr          : None
odfpy            : None
openpyxl         : None
pandas_gbq       : None
pyarrow          : None
pyxlsb           : None
s3fs             : None
scipy            : None
sqlalchemy       : None
tables           : None
tabulate         : 0.8.9
xarray           : None
xlrd             : None
xlwt             : None
numba            : None
```