Use read-only permissions for CMake CI workflow too

This wasn't done in 64add326f6 (Restrict job permissions in GitHub
actions workflows, 2022-06-27) for some reason.

See #22574.

Closes #22769.

Signed-off-by: sashashura <93376818+sashashura@users.noreply.github.com>

.github/workflows/ci_cmake.yml

@@ -45,6 +45,9 @@ on:
       - '*.yml'
       - 'wxwidgets.props'
 
+permissions:
+  contents: read
+
 jobs:
   build:
     runs-on: ${{ matrix.runner }}