Update comment about migrated mypy conf files

The change Ife39b55eb40c9cb8e61f1b2295b6d42cefe3a680 migrated mypy
configuration files from setup.cfg to pyproject.toml file, but a
comment in .pre-commit-config.yaml says to keep is in sync with
setup.cfg, which is incorrect.

This change updates comment in the .pre-commit-config.yaml file to
reflect the change.

Signed-off-by: Rajesh Tailor <ratailor@redhat.com>
Change-Id: I4d35b989e8c90b629bcb15438ad82f60f7ca8957

.pre-commit-config.yaml

@@ -64,7 +64,7 @@ repos:
       - id: mypy
         additional_dependencies:
           - types-paramiko
-        # keep this in-sync with '[mypy] files' in 'setup.cfg'
+        # keep this in-sync with '[tool.mypy] files' in 'pyproject.toml'
         files: |
           (?x)(
             nova/compute/manager.py