Fix evidence keeps a sentence's period after a quoted reproducer id #2743

Fix evidence failed two pull requests on 29 Oct 2026 because of how .github/check_fix_pr.py reads a Reproducer: line.

1. A sentence's period after a quoted id. #1969's line ended `…::test_x`.. _unquote_id strips backticks only when the value ends with one, so the last id kept both backticks and the period, and the check rejected it.

2. An unquoted YAML name with a comma. #2735's YAML test names contain commas. parse_reproducers splits unquoted ids at , and ;, so each name became two ids. Quoting the ids fixed it, but the failure message's hint never says to quote them.

parse_reproducers on main (2d437eb):

Reproducer: `policyengine_uk/tests/a.py::test_x`, `policyengine_uk/tests/b.py::test_y`.
  -> ['policyengine_uk/tests/a.py::test_x', '`policyengine_uk/tests/b.py::test_y`.']
Reproducer: policyengine_uk/tests/policy/x.yaml::NI household, no rebate
  -> ['policyengine_uk/tests/policy/x.yaml::NI household', 'no rebate']
Reproducer: `policyengine_uk/tests/policy/x.yaml::NI household, no rebate`
  -> ['policyengine_uk/tests/policy/x.yaml::NI household, no rebate']

Expected. A period right after a closing backtick ends the sentence and is not part of the id. An unquoted id keeps a trailing period, since a YAML test's name can end with one. The hint should say to put an id in backticks when its name contains a comma or semicolon.