Improve document for SyntaxWarning

[bebound]

Documentation

The SyntaxWarning appears only once during the pyc compilation, but I can't find this information in the documentation.

This is quite confusing for anyone trying to fix a SyntaxWarning. I noticed other warnings have descriptions like "ignored by default." Adding this information could help reduce confusion.

Related PR: #122844

Linked PRs

• gh-123858: Improve Doc: SyntaxWarning is emitted during bytecode generation #122844
• [3.13] gh-123858: Improve Doc: SyntaxWarning is emitted during bytecode generation (gh-122844) #138243
• [3.14] gh-123858: Improve Doc: SyntaxWarning is emitted during bytecode generation (gh-122844) #138244

[ncoghlan]

Backports are still pending, but I'm happy to consider this resolved. Thanks for the PR @bebound!