gh-151950: Fix unresolved AST references in ast.rst

[jx2lee]

This updates AST references in Doc/library/ast.rst that do not have Sphinx documentation targets. Prefixing the roles with ! preserves their semantic formatting while suppressing link generation. The constructor description now refers to AST node classes generally instead of the nonexistent ast.T.

The location-attributes paragraph is unchanged because it overlaps with PR #158039.

Testing:

• make -C Doc html SPHINXOPTS="-n" SOURCES=library/ast.rst still reports the two ast.expr and ast.stmt warnings in the unchanged paragraph.

• Issue: Fix Sphinx reference warnings in various Doc/library/ files #151950

[python-cla-bot]

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Documentation build overview

📚 cpython-previews | 🛠️ Build #34782421 | 📁 Comparing 5003b17 against main (b954645)

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10 files changed · ± 10 modified

± Modified

• c-api/init_config.html
• c-api/interp-lifecycle.html
• c-api/slice.html
• howto/free-threading-python.html
• library/argparse.html
• library/ast.html
• library/dis.html
• library/optparse.html
• whatsnew/3.16.html
• whatsnew/changelog.html