Update sphinx requirement from ~=8.2 to ~=8.1

---
updated-dependencies:
- dependency-name: sphinx
  dependency-version: 8.1.3
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

doc/requirements.txt

@@ -1,3 +1,3 @@
 -e .
-sphinx~=8.2
+sphinx~=8.1
 furo==2024.8.6