GHA: Switch some BE workflows to self-hosted runners (#109846)

* GHA: Use equivalent self-hosted runners for BE unit tests Enterprise

* GHA: Use standard runners for BE unit tests OSS

* GHA: Use equivalent self-hosted runner for ephemeral env action

* GHA: Use self-hosted runners and adjust shards for BE integration tests

* GHA: Upgrade BE integration test Postgres from 12 to 17

* GHA: Upgrade BE integration test MySQL from 8.0.32 to 8.0.43

.github/workflows/backend-unit-tests.yml

@@ -46,7 +46,7 @@ jobs:
       fail-fast: false
 
     name: Grafana (${{ matrix.shard }})
-    runs-on: ubuntu-latest-8-cores
+    runs-on: ubuntu-latest
     continue-on-error: true
     permissions:
       contents: read
@@ -81,7 +81,7 @@ jobs:
       fail-fast: false
 
     name: Grafana Enterprise (${{ matrix.shard }})
-    runs-on: ubuntu-latest-8-cores
+    runs-on: ubuntu-x64-large
     permissions:
       contents: read
       id-token: write