BLD: minor break ci/requirements-optional-pip.txt
- [x] closes #22595 
- [x] tests added / passed
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

When adding optional dependencies, below error appears from 

> Invalid requirement: 'openpyxl=2.5.5'
> = is not a valid operator. Did you mean == ?

To core dev, should we fix the version or simply specify lower bound (i.e. >=)?
Thanks for the PR @minggli. Those files are autogenerated. Can you check the comments in this PR: #22749 and fix in the source file please (and then autogenerate the ones you changed)? I think we want that specific version of openpyxl, so it'd be `openpyxl=2.5.5` (not `>=`). Can you confirm @TomAugspurger  # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/22889?src=pr&el=h1) Report
> Merging [#22889](https://codecov.io/gh/pandas-dev/pandas/pull/22889?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/e45a6c14fc969c31c46ae890e72883ffe6658b4e?src=pr&el=desc) will **increase** coverage by `0.02%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/22889/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/22889?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #22889      +/-   ##
==========================================
+ Coverage   92.18%   92.21%   +0.02%     
==========================================
  Files         169      169              
  Lines       50830    50975     +145     
==========================================
+ Hits        46860    47006     +146     
+ Misses       3970     3969       -1
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.63% <ø> (+0.02%)` | :arrow_up: |
| #single | `42.42% <ø> (+0.05%)` | :arrow_up: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/22889?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/22889/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `97.44% <0%> (+0.24%)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/22889?src=pr&el=continue).
> **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta)
> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/22889?src=pr&el=footer). Last update [e45a6c1...57ec327](https://codecov.io/gh/pandas-dev/pandas/pull/22889?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 Correct. We need to update `scripts/convert_deps.py` to rewrite exact pins as `==` for pip. > Thanks for the PR @minggli. Those files are autogenerated. Can you check the comments in this PR: #22749 and fix in the source file please (and then autogenerate the ones you changed)?

Thanks @datapythonista for looking into it. The `script/convert_deps.py` uses requirements-optional-conda.txt as base to generate, which has been fixed already.

```python3
with open("ci/requirements-optional-conda.txt") as f:
    optional = [x.strip() for x in f.readlines()]
```
so this should conclude the PR. Hello @minggli! Thanks for updating the PR.

 - There are no PEP8 issues in the file [`scripts/convert_deps.py`](https://github.com/minggli/pandas/blob/57ec32744640682765ba59885183a381940b09a5/scripts/convert_deps.py) !

 good point. thanks Marc. thanks. this is a dev requirement only. thanks for reviewing @jreback @datapythonista @TomAugspurger!