drop support for go1.19

Gomega no longer supports go1.19 so we cannot run tests without pinning
to an older release.

Go1.19 is EoL so stop testing with this version.

Updated test matrix to only test supported Go versions "stable"
(currently 1.21) and "oldstable" (1.20).

.github/workflows/run-tests.yml

@@ -15,15 +15,15 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        version: [ '1.19', '1.20' ]
+        version: [ 'oldstable', 'stable' ]
     name: Go ${{ matrix.version }}
     outputs:
       pr_number: ${{ github.event.number }}
     steps:
-    - uses: actions/setup-go@v2
+    - uses: actions/setup-go@v4
       with:
         go-version: ${{ matrix.version }}
-    - uses: actions/checkout@v2
+    - uses: actions/checkout@v4
     - run: ./scripts/run-tests.sh
   call-dependabot-pr-workflow:
     needs: test