Fix Dependabot pip update failure on sphinx requirement rewrite

[Copilot]

Dependabot’s pip update job was failing in the dynamic update run for this repository when processing sphinx, surfacing as an unknown_error with Expected content to change!. The failure came from requirement-line rewrite behavior, not dependency resolution.

• Root cause

  • Dependabot failed to rewrite the sphinx constraint line in requirements-doc.txt during grouped updates.

• Change

  • Normalized the sphinx specifier formatting in requirements-doc.txt to a compact, parser-friendly form used by Dependabot’s updater.

• Patch

  -sphinx>=9.0.4, <9.1.0
  +sphinx>=9.0.4,<9.1.0

• Impact

  • Keeps the same version bounds while removing the rewrite edge case that caused the Dependabot job to fail.