ci: add pip exclusion for msc/python test fixtures

The dependabot config missed /src/test/resources/msc/python in the pip
ecosystem exclusion, allowing security update PR guacsec#425 (mako bump) to be
created for an intentionally-pinned test fixture.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Author: ruromero

.github/dependabot.yml

@@ -43,6 +43,7 @@ updates:
     directories:
       - "/src/test/resources/tst_manifests/pip/**"
       - "/src/test/resources/tst_manifests/it/pypi/**"
+      - "/src/test/resources/msc/python"
     schedule:
       interval: "monthly"
     labels: []