gh-94808: Add test coverage for "starred kind" in _PyPegen_set_expr_context

[mjdominus]

gh-94808: Add test coverage for "starred kind" in _PyPegen_set_expr_context

That item is on the gh-94808 checklist, but not checked off. I ran lcov to confirm that the branch was not covered, added and ran the test, and rebuilt the coverage report to confirm that the branch had now been covered.

This pertains to the production

star_target[expr_ty] (memo):
| '*' a=(!'*' star_target) {
_PyAST_Starred(CHECK(expr_ty, _PyPegen_set_expr_context(p, a, Store)), Store,
EXTRA) }
| target_with_star_atom

at line 1057 in python.gram.

Thanks to @encukou for much guidance through this process.

[bedevere-app]

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[encukou]

Thank you!

[miss-islington-app]

Thanks @mjdominus for the PR, and @encukou for merging it 🌮🎉.. I'm working now to backport this PR to: 3.12, 3.13.
🐍🍒⛏🤖

[bedevere-app]

GH-119263 is a backport of this pull request to the 3.13 branch.

[bedevere-app]

GH-119264 is a backport of this pull request to the 3.12 branch.