gh-128409: Document that pdb.post_mortem() accepts exceptions

[adamchainz]

Fixes #128409.

• Issue: Document pdb.post_mortem() accepts exceptions on Python 3.13+ #128409

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📚 Documentation preview 📚: https://cpython-previews--128410.org.readthedocs.build/

[miss-islington-app]

Thanks @adamchainz for the PR, and @gaogaotiantian for merging it 🌮🎉.. I'm working now to backport this PR to: 3.13.
🐍🍒⛏🤖

[miss-islington-app]

Sorry, @adamchainz and @gaogaotiantian, I could not cleanly backport this to 3.13 due to a conflict.
Please backport using cherry_picker on command line.

cherry_picker 1b39b502d33c68f52fd775c4e6c2174baddd40bd 3.13

[bedevere-bot]

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot AMD64 CentOS9 NoGIL Refleaks 3.x has failed when building commit 1b39b50.

What do you need to do:

1. Don't panic.
2. Check the buildbot page in the devguide if you don't know what the buildbots are or how they work.
3. Go to the page of the buildbot that failed (https://buildbot.python.org/#/builders/1610/builds/653) and take a look at the build logs.
4. Check if the failure is related to this commit (1b39b50) or if it is a false positive.
5. If the failure is related to this commit, please, reflect that on the issue and make a new Pull Request with a fix.

You can take a look at the buildbot page here:

https://buildbot.python.org/#/builders/1610/builds/653

Failed tests:

• test_free_threading

Summary of the results of the build (if available):

==

Click to see traceback logs

remote: Enumerating objects: 5, done.        
remote: Counting objects:  25% (1/4)        
remote: Counting objects:  50% (2/4)        
remote: Counting objects:  75% (3/4)        
remote: Counting objects: 100% (4/4)        
remote: Counting objects: 100% (4/4), done.        
remote: Compressing objects:  50% (1/2)        
remote: Compressing objects: 100% (2/2)        
remote: Compressing objects: 100% (2/2), done.        
remote: Total 5 (delta 2), reused 2 (delta 2), pack-reused 1 (from 1)        
From https://github.com/python/cpython
 * branch                    main       -> FETCH_HEAD
Note: switching to '1b39b502d33c68f52fd775c4e6c2174baddd40bd'.

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  git switch -c <new-branch-name>

Or undo this operation with:

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Turn off this advice by setting config variable advice.detachedHead to false

HEAD is now at 1b39b502d33 gh-128409: Document that pdb.post_mortem() accepts exceptions (#128410)
Switched to and reset branch 'main'

configure: WARNING: no system libmpdecimal found; falling back to bundled libmpdecimal (deprecated and scheduled for removal in Python 3.15)

make: *** [Makefile:2322: buildbottest] Error 2