TST: Remove fsspec internals from tests
- [ ] closes #xxxx (Replace xxxx with the GitHub issue number)
- [ ] [Tests added and passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#writing-tests) if fixing a bug or adding a new feature
- [ ] All [code checks passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#pre-commit).
- [ ] Added [type annotations](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#type-hints) to new arguments/methods/functions.
- [ ] Added an entry in the latest `doc/source/whatsnew/vX.X.X.rst` file if fixing a bug or adding a new feature.

I don't think clearing the registry does anything. The public registry var is supposed to be immutable, and we were just clearing the internal registry dict. 

However, we didn't remove gcs from the known_implementations dict, so gcs would've technically still been in the registry IIUC this code correctly. 

https://github.com/fsspec/filesystem_spec/blob/0f3ecd8e629043646ab19b1a2b00d895f0553a81/fsspec/registry.py#L206-L209

CircleCI failure is separate and unrelated. Owee, I'm MrMeeseeks, Look at me.

There seem to be a conflict, please backport manually. Here are approximate instructions:

1. Checkout backport branch and update it.

```
git checkout 1.5.x
git pull
```

2. Cherry pick the first parent branch of the this PR on top of the older branch:
```
git cherry-pick -x -m1 ce9e3d658d6efa3600a4563ca7a00e7a15b80272
```

3. You will likely have some merge/cherry-pick conflict here, fix them and commit:

```
git commit -am 'Backport PR #50925: TST: Remove fsspec internals from tests'
```

4. Push to a named branch:

```
git push YOURFORK 1.5.x:auto-backport-of-pr-50925-on-1.5.x
```

5. Create a PR against branch 1.5.x, I would have named this PR:

> "Backport PR #50925 on branch 1.5.x (TST: Remove fsspec internals from tests)"

And apply the correct labels and milestones.

Congratulations — you did some good work! Hopefully your backport PR will be tested by the continuous integration and merged soon!

Remember to remove the `Still Needs Manual Backport` label once the PR gets merged.

If these instructions are inaccurate, feel free to [suggest an improvement](https://github.com/MeeseeksBox/MeeseeksDev).
                 thx @lithomas1, could you backport manually? backported in #51038