PR: Update PyQt requirement to 5.15

[ccordoba12]

Description of Changes

• This is finally the time to do it because we're going to have PyQt 5.15 packages available in conda-forge, thanks to @andfoy's work.
• I expect this to take some time because our test suite is big.

Issue(s) Resolved

Fixes #17197
Fixes #17085
Fixes #17083
Fixes #17060
Fixes #12829

Affirmation

By submitting this Pull Request or typing my (user)name below,
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.

I certify the above statement is true and correct: @ccordoba12

[rear1019]

check_qt() in spyder/requirements.py must be updated as well.

[juliangilbey]

Just looking at the changes, I wonder whether you could include more recent Pythons in the testing (the current version in the tests is 3.7)? The current Python version is 3.10, while 3.8 was released over two years ago.

[pep8speaks]

Hello @ccordoba12! Thanks for updating this PR. We checked the lines you've touched for PEP 8 issues, and found:

There are currently no PEP 8 issues detected in this Pull Request. Cheers! 🍻

Comment last updated at 2022-03-17 17:20:03 UTC

[ccordoba12]

@dalthviz, please rebase to get the fixes for our tests I pushed last weekend. With them, you can check if the fast tests actually fisnish.

[ccordoba12]

@dalthviz, I skipped spyder/plugins/onlinehelp/tests/test_pydocgui.py::test_get_pydoc in PR #17288 because it was failing too much.

Since you fixed it here, please renable it after a rebase.

[ccordoba12]

Thanks a lot @dalthviz for your hard work on this!

It looks pretty good to me, except for the minor comments I left for you below.

[ccordoba12]

Last minor nitpick @dalthviz, then this should be finally ready!!

[ccordoba12]

Thanks again @dalthviz! Great work here!!