[Backport maintenance/4.0.x] Support isort 9 (#11354)

Support isort 9 (#11352)

Closes #11351

(cherry picked from commit 48d3c54)

Author: Pierre-Sassoulas

doc/whatsnew/fragments/11351.other

@@ -0,0 +1,3 @@
+Upgrade the ``isort`` upper bound so ``isort`` 9 can be installed alongside pylint.
+
+Closes #11351

pyproject.toml

@@ -45,7 +45,7 @@ dependencies = [
   "dill>=0.2; python_version<'3.11'",
   "dill>=0.3.6; python_version>='3.11'",
   "dill>=0.3.7; python_version>='3.12'",
-  "isort>=5,!=5.13,<9",
+  "isort>=5,!=5.13,<10",
   "mccabe>=0.6,<0.8",
   "platformdirs>=2.2",
   "tomli>=1.1; python_version<'3.11'",