ci: split pgsql shards into plain jobs, dedupe setup actions (#37802)

1. Split the psql matrix jobs into composite actions. Matrix jobs that
can skip do not work with required checks on GitHub because skipped and
unskipped emit different job names (GitHub bug
https://github.com/orgs/community/discussions/9141).
2. Dedupe node and go setup steps into composite actions

Currently test-psql branch protection is disabled, will re-enable when
merging this.

---------

Signed-off-by: silverwind <me@silverwind.io>
Co-authored-by: Claude (Opus 4.7) <noreply@anthropic.com>
Co-authored-by: Nicolas <bircni@icloud.com>

.github/actions/pgsql-shard/action.yml

@@ -0,0 +1,40 @@
+name: pgsql-shard
+description: Run one pgsql integration test shard
+
+inputs:
+  shard:
+    description: Shard index
+    required: true
+  total-shards:
+    description: Total shard count
+    required: true
+  run-migration:
+    description: Also run migration tests
+    default: "false"
+
+runs:
+  using: composite
+  steps:
+    - name: Add hosts to /etc/hosts
+      shell: bash
+      run: '[ -e "/.dockerenv" ] || [ -e "/run/.containerenv" ] || echo "127.0.0.1 pgsql ldap minio" | sudo tee -a /etc/hosts'
+    - shell: bash
+      run: make deps-backend
+    - shell: bash
+      run: make backend
+      env:
+        TAGS: bindata
+    - name: run migration tests
+      if: ${{ inputs.run-migration == 'true' }}
+      shell: bash
+      run: GITEA_TEST_DATABASE=pgsql make test-migration
+    - name: run tests
+      shell: bash
+      run: GITEA_TEST_DATABASE=pgsql make test-integration
+      env:
+        # pgsql is chosen to be the unlucky one to run with the slow "race detector", it is about 60% slower.
+        GOTEST_FLAGS: -race -timeout=40m
+        TAGS: bindata gogit
+        TEST_LDAP: 1
+        TEST_SHARD: ${{ inputs.shard }}
+        TEST_TOTAL_SHARDS: ${{ inputs.total-shards }}