Fix Deprecation Warnings in 'Check USNs' Workflow.

Fix deprecation warnings for actions using a deprecated version of node.
Also switch to a fixed version of the environment in order to avoid
future deprecation warnings.

Signed-off-by: Michael Keller <github@ike.ch>

.github/workflows/snap_usns.yml

@@ -7,28 +7,28 @@ on:
 
 jobs:
   CheckUSNs:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-22.04
 
     steps:
     - name: Check out code
-      uses: actions/checkout@v2
+      uses: actions/checkout@v4
 
     - name: Set up Python
-      uses: actions/setup-python@v2
+      uses: actions/setup-python@v4
       with:
         python-version: '3.x'
 
     - name: Install Python dependencies
-      uses: BSFishy/pip-action@v1
+      uses: brettcannon/pip-secure-install@v1
       with:
-        requirements: .github/workflows/scripts/requirements.txt
+        requirements-file: .github/workflows/scripts/requirements.txt
 
     - name: Install Snap dependencies
       run: |
         sudo snap install review-tools --edge
 
     - name: Set up Launchpad credentials
-      uses: DamianReeves/write-file-action@v1.0
+      uses: DamianReeves/write-file-action@v1
       with:
         path: lp_credentials
         contents: ${{ secrets.LAUNCHPAD_CREDENTIALS }}