Replace "foo!r" to "repr(foo)" syntax
Since we are moving to f-strings and dropping old strings formats (```%``` and ```.format()```), we no longer need to have the redundant ```%r``` and ```!r``` specifiers, instead we use the ```repr()``` format.

#### Notes:
* Don't forget to link this issue in your PR, paste this ```https://github.com/pandas-dev/pandas/issues/29886``` in your PR.

* If any of your changed files are related to #29547 , please make sure to link your pull request to that issue as well, simply paste this ```https://github.com/pandas-dev/pandas/issues/29547``` in your pull request's body message as well.

* Please comment what you are planning to work on, so we won't do double work.

* If a file/files that should be marked as done, is'nt marked, please comment letting me know.

---

To check what files still needs to be fixed in the "pandas" directory:
```
grep -R -e '%r' -e '!r}' -e "'{}'" --include=*.{py,pyx} pandas/
```

##### Tip:
If you want to see the line number of the occurrence, replace the ```-l``` with ```-n```
for example:
```
grep -n -R '%r' --include=*.{py,pyx} pandas/
```

---

### The current list is:

- [x] ci/print_skipped.py

- [x] pandas/_config/config.py

- [x] pandas/conftest.py

- [x] pandas/core/accessor.py

- [x] pandas/core/algorithms.py

- [x] pandas/core/arrays/categorical.py

- [ ] pandas/core/arrays/datetimelike.py

- [ ] pandas/core/arrays/period.py

- [x] pandas/core/arrays/numpy_.py

- [x] pandas/core/computation/align.py

- [x] pandas/core/computation/eval.py

- [x] pandas/core/computation/expressions.py

- [x] pandas/core/computation/expr.py

- [x] pandas/core/computation/ops.py

- [x] pandas/core/computation/pytables.py

- [x] pandas/core/dtypes/common.py

- [x] pandas/core/dtypes/dtypes.py

- [x] pandas/core/frame.py

- [x] pandas/core/generic.py

- [x] pandas/core/groupby/grouper.py

- [x] pandas/core/indexes/base.py

- [x] pandas/core/indexes/datetimelike.py

- [x] pandas/core/indexes/interval.py

- [x] pandas/core/indexes/numeric.py

- [x] pandas/core/internals/concat.py

- [x] pandas/core/internals/managers.py

- [x] pandas/core/missing.py

- [x] pandas/core/nanops.py

- [x] pandas/core/reshape/concat.py

- [x] pandas/core/reshape/merge.py

- [x] pandas/core/reshape/tile.py

- [x] pandas/core/series.py

- [x] pandas/core/sorting.py

- [x] pandas/core/strings.py

- [x] pandas/core/window/rolling.py

- [x] pandas/\_\_init\_\_.py

- [x] pandas/io/formats/css.py

- [x] pandas/io/formats/excel.py

- [ ] pandas/io/formats/style.py

- [x] pandas/io/html.py

- [x] pandas/io/parsers.py

- [x] pandas/_libs/interval.pyx

- [x] pandas/plotting/_core.py

- [x] pandas/tests/computation/test_eval.py

- [x] pandas/tests/frame/test_alter_axes.py

- [x] pandas/tests/frame/test_analytics.py

- [x] pandas/tests/frame/test_query_eval.py

- [x] pandas/tests/groupby/test_whitelist.py

- [x] pandas/tests/indexes/datetimes/test_datetime.py

- [x] pandas/tests/indexes/multi/test_integrity.py

- [x] pandas/tests/indexes/period/test_period.py

- [x] pandas/tests/indexes/test_common.py

- [ ] pandas/tests/indexes/timedeltas/test_timedelta.py

- [x] pandas/tests/io/msgpack/test_case.py

- [x] pandas/tests/io/msgpack/test_extension.py

- [x] pandas/tests/io/parser/test_unsupported.py

- [x] pandas/tests/io/test_html.py

- [x] pandas/tests/test_expressions.py

- [x] pandas/tests/test_strings.py

- [ ] pandas/tests/io/test_sql.py

- [ ] pandas/tests/reshape/test_concat.py

- [ ] pandas/tests/scalar/timedelta/test_timedelta.py

- [x] pandas/tests/series/test_missing.py

- [x] pandas/tests/tseries/offsets/test_fiscal.py

- [x] pandas/tests/tseries/offsets/test_offsets.py

- [x] pandas/tseries/offsets.py

- [x] pandas/util/_decorators.py

- [x] pandas/util/_test_decorators.py

- [x] pandas/util/testing.py

- [x] pandas/_version.py

- [ ] /scripts/tests/test_validate_docstrings.py
---

#### Lastly:
- [ ] Add a test case (so we won't regress)