Add tfsec working directory

* There is a bug in tfsec, where it finds vulnerabilities, but just
  outputs 'Ignoring - change not part of the current PR' - Even though
  it is. This is causing the check to pass, when it should fail.
* Adding `working_directory: ''` fixes the issue
* aquasecurity/tfsec-pr-commenter-action#90 (comment)

.github/workflows/continuous-integration-tfsec.yml

@@ -12,3 +12,4 @@ jobs:
         uses: aquasecurity/[email protected]
         with:
           github_token: ${{ github.token }}
+          working_directory: ''