Automatic part of merging branch 'master' into sh_merge_master.

The only manual intervention was to remove the merge conflict markers in pybind11.h.

TODO in separate commit: complete removal of the obsolete detail/pragma_warning_block.h.

.pre-commit-config.yaml

@@ -32,10 +32,15 @@ repos:
     exclude: ^noxfile.py$
 
 - repo: https://github.com/asottile/pyupgrade
-  rev: v2.23.0
+  rev: v2.23.3
   hooks:
   - id: pyupgrade
 
+- repo: https://github.com/PyCQA/isort
+  rev: 5.9.3
+  hooks:
+  - id: isort
+
 # Black, the code formatter, natively supports pre-commit
 - repo: https://github.com/psf/black
   rev: 21.7b0