PR: Fix enabled state of Run plugin actions when a file type doesn't have an associated configuration

[ccordoba12]

Description of Changes

• This problem occurred, for instance, when the last file to receive focus after Spyder started was a Markdown one. And that's because those files don't have a run configuration associated to them by default.
• Also, improve a couple of block comments in BaseEditMixin.

Issue(s) Resolved

Fixes #22607

Affirmation

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I affirm the Developer Certificate of Origin
with respect to all commits and content included in this PR,
and understand I am releasing the same under Spyder's MIT (Expat) license.

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[ccordoba12]

@meeseeksdev please backport to 6.x

[lumberbot-app]

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 6.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 0e71cda83cf4cfdeef17e63a485598801f66f40e

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

git commit -am "Backport PR #22819: PR: Fix enabled state of Run plugin actions when a file type doesn't have an associated configuration"

4. Push to a named branch:

git push YOURFORK 6.x:auto-backport-of-pr-22819-on-6.x

5. Create a PR against branch 6.x, I would have named this PR:

"Backport PR #22819 on branch 6.x (PR: Fix enabled state of Run plugin actions when a file type doesn't have an associated configuration)"

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.