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/node-setup/action.yml

@@ -0,0 +1,22 @@
+name: node-setup
+description: Set up pnpm and node and restore caches
+
+inputs:
+  cache:
+    description: Cache pnpm downloads
+    default: "true"
+
+runs:
+  using: composite
+  steps:
+    - uses: pnpm/action-setup@0e279bb959325dab635dd2c09392533439d90093 # v6.0.8
+    - if: ${{ inputs.cache == 'true' }}
+      uses: actions/setup-node@48b55a011bda9f5d6aeb4c2d9c7362e8dae4041e # v6.4.0
+      with:
+        node-version: 24
+        cache: pnpm
+        cache-dependency-path: pnpm-lock.yaml
+    - if: ${{ inputs.cache != 'true' }}
+      uses: actions/setup-node@48b55a011bda9f5d6aeb4c2d9c7362e8dae4041e # v6.4.0
+      with:
+        node-version: 24