Strip ANSI sequences before writing junitxml text

[00200200]

Problem

Closes #12365. With Pygments installed and color enabled, assertion diffs under -v/-vv embed ANSI SGR sequences into longrepr. Those leak into --junitxml as #x1B[...] fragments and break CI XML consumers.

Fix

Strip SGR escape sequences at the junitxml write boundary (failure/error message and details) before bin_xml_escape. This keeps TerminalRepr untouched for cases where user data intentionally contains escapes (which saferepr already renders as literal \x1b text).

How tested

testing/test_junitxml.py::test_junitxml_strips_ansi_from_failure_details (with pygments, PY_COLORS=1, -vv).

[ege-arhan]

_write_content (src/_pytest/junitxml.py:206-208 on head 6229b1e) still writes captured output via bin_xml_escape(content) without strip_ansi_escapes. Repro on pytest 9.1.1: a test printing "\x1b[31mred\x1b[0m" with --junitxml out.xml -o junit_logging=all leaves #x1B[31m...#x1B[0m inside <system-out> (verified by parsing the XML). The new test only covers failure details. Suggestion: apply strip_ansi_escapes(content) in _write_content too, or narrow the changelog if captured output is intentionally left verbatim.

[00200200]

Thanks @ege-arhan, you're right. _write_content now applies strip_ansi_escapes as well, so captured output in <system-out>/<system-err> is cleaned too, and the changelog says so. Added test_ansi_escapes_stripped_from_captured_output (fails without the change, passes with it). The macOS failures came from test_escaped_setup_teardown_error still asserting the old escaped form; it now asserts the stripped text. testing/test_junitxml.py passes locally (143) and pre-commit is clean.