Bump Go version to v1.20 (#24439)

.github/workflows/server-test-template.yml

@@ -15,14 +15,14 @@ on:
         required: true
         type: string
 env:
-  go-version: "1.19.5"
+  go-version: "1.20.7"
 jobs:
   test:
     name: ${{ inputs.name }}
     runs-on: ubuntu-latest-8-cores
     env:
       COMPOSE_PROJECT_NAME: ghactions
-      BUILD_IMAGE: mattermost/mattermost-build-server:20230118_golang-1.19.5
+      BUILD_IMAGE: mattermost/mattermost-build-server:20230904_golang-1.20.7
     steps:
       - name: Checkout mattermost project
         uses: actions/checkout@ac593985615ec2ede58e132d2e21d2b1cbd6127c # v3.3.0