Lock down requirements file

.github/workflows/verify-locked-down-signatures.yml

@@ -30,6 +30,7 @@ on:
       - android/gradle/wrapper/gradle-wrapper.jar
       - android/gradle/wrapper/gradle-wrapper.properties
       - android/scripts/lockfile
+      - android/docker/requirements.txt
       - flake.lock
       - building/build-and-publish-container-image.sh
       - building/mullvad-app-container-signing.asc