separate subtests failures to give better indication on tests analysis

[RoniKishner]

Description

This PR fixes the double-counting of subtest failures in pytest's final test summary. Previously, when a test with subtests had failures, both the subtest failure and the top-level test failure were counted as regular "failed" tests, leading to inflated failure counts.

Changes

• Modified pytest_report_teststatus hook in src/_pytest/subtests.py to return "subtests failed" category instead of "failed" for subtest failures
• Updated _determine_main_color in src/_pytest/terminal.py to consider "subtests failed" when determining the main color (red)
• Enhanced parse_summary_nouns in src/_pytest/pytester.py:
  • Updated regex to handle multi-word outcomes like "subtests failed"
  • Added pluralization mapping for subtest outcomes
  • Added whitespace handling for parsed outcomes
• Updated test expectations in testing/test_subtests.py to match the new summary format

Example

Before:
===================== 2 failed, 2 subtests passed in 0.02s =====================
After:
===================== 1 failed, 2 subtests passed, 1 subtests failed in 0.02s =====================

This provides clear visibility into:

• How many top-level tests failed (1 failed)
• How many subtests failed (1 subtests failed)
• How many subtests passed (2 subtests passed)

Closes #13986

[nicoddemus]

Thanks @RoniKishner for the PR.

I'm OK with separating subtest failures from normal failures.

I left a suggestion regarding the changelog, could you also take a look at the failing tests?

[nicoddemus]

@RoniKishner the tests are still failing, do you need help with that?