doctest_docutils(fix[regex]): Backport doctestopt_re whitespace fix

Backport: Sphinx commit ad0c343d3 (2025-01-04)
Ref: sphinx-doc/sphinx@ad0c343d3

why: Doctest directive comments with leading whitespace were not recognized
what:
- Add [ \t]* prefix to doctestopt_re pattern
- Allows doctest options like "  # doctest: +SKIP" to be properly parsed
- Fixes edge case where indented doctest directive comments were ignored

Author: tony

src/doctest_docutils.py

@@ -30,7 +30,10 @@
 
 
 blankline_re = re.compile(r"^\s*<BLANKLINE>", re.MULTILINE)
-doctestopt_re = re.compile(r"#\s*doctest:.+$", re.MULTILINE)
+# Backported from Sphinx commit ad0c343d3 (2025-01-04).
+# https://github.com/sphinx-doc/sphinx/commit/ad0c343d3
+# Allow optional leading whitespace before doctest directive comments.
+doctestopt_re = re.compile(r"[ \t]*#\s*doctest:.+$", re.MULTILINE)
 
 
 def is_allowed_version(version: str, spec: str) -> bool: