FIX: Pin rstcheck to prevent CI failure

While rstcheck itself is frozen and also was not updated, it depends on
rstcheck-core, which was recently updated to 1.3 and contains a bug
that results in a false error.

rstcheck/rstcheck-core#114 (review)

This PR excludes that version to fix pre-commit rstcheck in our CI.

Author: timhoffm

.pre-commit-config.yaml

@@ -70,6 +70,7 @@ repos:
     hooks:
       - id: rstcheck
         additional_dependencies:
+          - rstcheck-core!=1.3  # https://github.com/rstcheck/rstcheck-core/pull/114#pullrequestreview-4239740896
           - sphinx>=1.8.1
           - tomli
   - repo: https://github.com/adrienverge/yamllint