test(git): pin the glued -n<N> form of the git log limit

[guyoron1]

Summary

Refs #2665

rtk git log -n20 used to return 10 commits because the glued -n<N> form wasn't recognised. That was fixed on develop by the shared arg tokenizer (#3681), so the code change this PR originally carried is obsolete and has been dropped.

What is left is the coverage, since nothing on develop pins the glued form (the existing tests cover -20, -n 15 and --max-count):

• test_parse_user_limit_n_combined (parser + has_limit_flag)
• -n20 added to the shapes in a_user_limit_or_a_revision_range_is_not_capped (raw path)
• a_glued_n_limit_is_the_users_limit_on_the_compact_listing (compact path: unbounded = 10; -n20, -n 20 and -20 = 20)

All three fail if the reported bug is reintroduced (checked by making -n count only when its value is a separate token). Issue #2665 itself is fixed on develop and can be closed.

• cargo fmt --all -- --check, cargo clippy --all-targets (0 warnings), cargo test --all (all pass)

[guyoron1]

Checked against current develop: rtk git log -n20 now returns 20 commits (it returned 10 before the arg tokenizer in #3681), so the code fix here is obsolete and I've dropped it. Nothing on develop pins the glued -n<N> form though, so this is now a tests-only PR (retitled, and Refs instead of Fixes). The tests fail if the bug is reintroduced. Feel free to close it if you'd rather not carry the extra tests.

#2665 itself is fixed on develop and can be closed. #4148 and #4152 also edit tests/git_log_cap_notice_test.rs, so expect a small textual conflict in that file for whichever lands second.