Fix Github Actions on self-hosted (#180)

## 🎫 Ticket

N/A

## 🛠 Changes

- Add env var to fix self-hosted Github Actions steps.

## ℹ️ Context

See actions/checkout#1809 for technical
context.

<!-- If any of the following security implications apply, this PR must
not be merged without Stephen Walter's approval. Explain in this section
and add @SJWalter11 as a reviewer.
  - Adds a new software dependency or dependencies.
  - Modifies or invalidates one or more of our security controls.
  - Stores or transmits data that was not stored or transmitted before.
- Requires additional review of security implications for other reasons.
-->

## 🧪 Validation

Sonarqube quality check passes on this PR.

.github/workflows/ci-workflow.yml

@@ -41,6 +41,9 @@ jobs:
     name: Sonarqube Quality Gate
     needs: build
     runs-on: self-hosted
+    env:
+      # Workaround until https://jira.cms.gov/browse/PLT-338 is implemented.
+      ACTIONS_ALLOW_USE_UNSECURE_NODE_VERSION: "true"
     steps:
       - name: Download code coverage
         uses: actions/download-artifact@v2