Fix check-rst-files hook to work cross-platform

.pre-commit-config.yaml

@@ -55,7 +55,7 @@ repos:
     hooks:
     -   id: check-rst-files
         name: Check for .rst files in the top-level directory
-        entry: sh -c 'ls *.rst 1>/dev/null 2>&1 && { echo "found .rst file in top-level folder"; exit 1; } || exit 0'
+        entry: python -c "import glob, sys; rst_files = glob.glob('*.rst'); sys.exit(1) if rst_files else sys.exit(0)"
         language: system
         always_run: true
         pass_filenames: false