test.support.requires_debug_ranges raise SkipTest not returning decorator when `_testcapi` doesn't exist

[youknowone]

Bug report

Bug description:

@requires_debug_ranges()
class ...:

requires_debug_ranges here is expected to skip the decorated test. But when _testcapi doesn't exist, it raises unittest.SkipTest when calling the decorator.

CPython versions tested on:

CPython main branch

Operating systems tested on:

No response

Linked PRs

• GH-137194 Fix requires_debug_ranges when _testcpi doesn't exist #137195
• [3.14] gh-137194: Fix requires_debug_ranges when _testcpi doesn't exist (GH-137195) #137274
• [3.13] gh-137194: Fix requires_debug_ranges when _testcpi doesn't exist (GH-137195) #137275