gh-133033: Add document for TypeIgnore

[koyuki7w]

Fixes gh-133033

---

📚 Documentation preview 📚: https://cpython-previews--133034.org.readthedocs.build/

[sobolevn]

Thank you!

[miss-islington-app]

Thanks @koyuki7w for the PR, and @sobolevn for merging it 🌮🎉.. I'm working now to backport this PR to: 3.13.
🐍🍒⛏🤖

[bedevere-app]

GH-133078 is a backport of this pull request to the 3.13 branch.

[bedevere-bot]

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot AMD64 CentOS9 NoGIL Refleaks 3.13 (tier-1) has failed when building commit 6ade0c3.

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/1605/builds/707) and take a look at the build logs.
4. Check if the failure is related to this commit (6ade0c3) 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/1605/builds/707

Failed tests:

• test_free_threading

Test leaking resources:

• test_free_threading: memory blocks

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

==

Click to see traceback logs

remote: Enumerating objects: 5, done.        
remote: Counting objects:  20% (1/5)        
remote: Counting objects:  40% (2/5)        
remote: Counting objects:  60% (3/5)        
remote: Counting objects:  80% (4/5)        
remote: Counting objects: 100% (5/5)        
remote: Counting objects: 100% (5/5), done.        
remote: Total 5 (delta 4), reused 4 (delta 4), pack-reused 0 (from 0)        
From https://github.com/python/cpython
 * branch                    3.13       -> FETCH_HEAD
Note: switching to '6ade0c3b2b51b56e68777658d4373d9b80cbdd54'.

You are in 'detached HEAD' state. You can look around, make experimental
changes and commit them, and you can discard any commits you make in this
state without impacting any branches by switching back to a branch.

If you want to create a new branch to retain commits you create, you may
do so (now or later) by using -c with the switch command. Example:

  git switch -c <new-branch-name>

Or undo this operation with:

  git switch -

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

HEAD is now at 6ade0c3b2b5 [3.13] gh-133033: Add docs for `TypeIgnore` (GH-133034) (#133078)
Switched to and reset branch '3.13'

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

make: *** [Makefile:2241: buildbottest] Error 2