Add schedule trigger to "Check Go Dependencies" workflow

The workflow is configured to run whenever any relevant file in the repository is changed. However, the results of the
workflow run are also dependent on the external environment it runs in, which include:

- The software running on the GitHub hosted GitHub Actions runner machines
- The GitHub Actions actions used by the workflow
- The dependencies that are installed by the workflow directly or via the GitHub Actions actions it uses

The workflow does not fully pin to a specific version of external tools. This was done in the interest of reducing the
maintenance burden of keeping the systems up to date. However, it also means that a new release of one of those tools
can cause the workflow runs to start failing (which might happen through an enhancement to that resource resolving a
false negative, or a defect causing a false negative).

When the repository file path trigger is used by itself, this sort of external breakage is only revealed when an
unrelated change triggers the workflow. That can be distracting even to a dedicated member of the project development
team, as well as confusing and discouraging to any contributor.

This type of change can be caught by adding a `schedule` event trigger that causes the workflow to run periodically in
addition to the other on-demand triggers. This allows the problem to be identified and resolved at the maintainer's
convenience, separate from the unrelated development work.

.github/workflows/check-go-dependencies-task.yml

@@ -27,6 +27,9 @@ on:
       - "**/.gitmodules"
       - "**/go.mod"
       - "**/go.sum"
+  schedule:
+    # Run periodically to catch breakage caused by external changes.
+    - cron: "0 8 * * WED"
   workflow_dispatch:
   repository_dispatch: