Add concurrency group to ci.yml

While at it, bump go-version to go1.22 and go1.23
and remove older versions from list.

.github/workflows/ci.yml

@@ -18,6 +18,10 @@ on:
     - 'feature/**'
     - 'v**'
 
+concurrency:
+  group: ${{ github.workflow }}-${{ github.event.pull_request.number || github.run_id }}
+  cancel-in-progress: true
+
 jobs:
 
   # Test on various OS with default Go version. 
@@ -31,7 +35,7 @@ jobs:
     strategy:
       matrix:
         os: [ubuntu-latest]
-        go-version: ['1.20', 1.21, 1.22]
+        go-version: ['1.22', '1.23']
 
     steps:
     - name: Install Go