ci: collect coverage inline on Postgres job, remove duplicate Coverage job (#36216)

The Coverage job ran the same tests as Postgres with only ENABLE_COVERAGE=true
and a Codecov upload as differences. Enable coverage directly on the Postgres
job under the same release-branch skip condition, eliminating 4x 8-core runner
hours per PR.

.github/workflows/server-ci.yml

@@ -215,6 +215,7 @@ jobs:
       drivername: postgres
       # Each shard gets a unique artifact name so they don't collide
       logsartifact: "postgres-server-test-logs-shard-${{ matrix.shard }}"
+      enablecoverage: ${{ github.event_name != 'pull_request' || !startsWith(github.event.pull_request.base.ref, 'release-') }}
       go-version: ${{ needs.go.outputs.version }}
       fips-enabled: false
       shard-index: ${{ matrix.shard }}
@@ -275,29 +276,6 @@ jobs:
       artifact-pattern: postgres-server-fips-test-logs-shard-*
       artifact-name: postgres-server-fips-test-logs
 
-  test-coverage:
-    name: "Coverage (shard ${{ matrix.shard }})"
-    if: ${{ github.event_name != 'pull_request' || !startsWith(github.event.pull_request.base.ref, 'release-') }}
-    needs: go
-    strategy:
-      fail-fast: false
-      matrix:
-        shard: [0, 1, 2, 3]
-    uses: ./.github/workflows/server-test-template.yml
-    secrets: inherit
-    with:
-      name: "Coverage (shard ${{ matrix.shard }})"
-      datasource: postgres://mmuser:mostest@postgres:5432/mattermost_test?sslmode=disable&connect_timeout=10
-      drivername: postgres
-      logsartifact: "coverage-server-test-logs-shard-${{ matrix.shard }}"
-      fullyparallel: true
-      allow-failure: true
-      enablecoverage: true
-      go-version: ${{ needs.go.outputs.version }}
-      fips-enabled: false
-      # runner: ubuntu-22.04 # Coverage is non-blocking (allow-failure), no need for 8-core
-      shard-index: ${{ matrix.shard }}
-      shard-total: 4
   test-mmctl:
     name: Run mmctl tests
     needs: go