BUG: Incorrect timedelta with tz_localize and nonexistent times
- [x] I have checked that this issue has not already been reported.

- [x] I have confirmed this bug exists on the latest version of pandas.

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

---

#### Code Sample, a copy-pastable example

```python
s = pd.Series(range(2),
              index=pd.DatetimeIndex(['2021-03-28 01:30:00',
                                      '2021-03-28 02:30:00']))
s.tz_localize('Europe/London', nonexistent=pd.Timedelta('1H'))
```
```python
2021-03-28 03:30:00+01:00    0
2021-03-28 02:30:00+01:00    1
dtype: int64
```
#### Problem description

Using Timedelta with the `nonexistent` flag with `tz_localize` is adding 2 hours instead of 1 hour for nonexistent times in 'Europe/London' tz. DST started on 2021-03-28 when 59:59 > 02:00 so '2021-03-28 01:30:00' is nonexistent. When I run almost the same code from the docs with 'Europe/Warsaw' the bug does not occur:

```python
s = pd.Series(range(2),
              index=pd.DatetimeIndex(['2021-03-28 02:30:00',
                                      '2021-03-28 03:30:00']))
s.tz_localize('Europe/Warsaw', nonexistent=pd.Timedelta('1H'))
```
```python
2021-03-28 03:30:00+02:00    0
2021-03-28 03:30:00+02:00    1
dtype: int64
```

#### Expected Output
```python
2021-03-28 02:30:00+01:00    0
2021-03-28 02:30:00+01:00    1
dtype: int64
```

#### Output of ``pd.show_versions()``

<details>

INSTALLED VERSIONS
------------------
commit           : f2c8480af2f25efdbd803218b9d87980f416563e
python           : 3.8.7.final.0
python-bits      : 64
OS               : Windows
OS-release       : 10
Version          : 10.0.18362
machine          : AMD64
processor        : Intel64 Family 6 Model 158 Stepping 9, GenuineIntel
byteorder        : little
LC_ALL           : None
LANG             : None
LOCALE           : English_United Kingdom.1252

pandas           : 1.2.3
numpy            : 1.19.5
pytz             : 2020.5
dateutil         : 2.8.1
pip              : 20.3.3
setuptools       : 51.1.2
Cython           : None
pytest           : None
hypothesis       : None
sphinx           : None
blosc            : None
feather          : None
xlsxwriter       : None
lxml.etree       : None
html5lib         : None
pymysql          : None
psycopg2         : None
jinja2           : 2.11.2
IPython          : 7.19.0
pandas_datareader: None
bs4              : None
bottleneck       : None
fsspec           : None
fastparquet      : None
gcsfs            : None
matplotlib       : None
numexpr          : None
odfpy            : None
openpyxl         : 3.0.6
pandas_gbq       : None
pyarrow          : 2.0.0
pyxlsb           : None
s3fs             : None
scipy            : None
sqlalchemy       : None
tables           : None
tabulate         : None
xarray           : None
xlrd             : None
xlwt             : None
numba            : None

</details>
