fix: use docker postgres:18 for pg_dump/psql to fix version mismatch (#28260)

The recent upgrade to PostgreSQL 18 in CI (commit 27515d4) caused the
Setup Database job to fail because the runner's host pg_dump (v16) refuses
to dump a Postgres 18 server.

Replace tj-actions/pg-dump and tj-actions/pg-restore with docker run
commands using the postgres:18 image, ensuring the client version always
matches the server. This aligns with the fix already applied in the
internal cal repo.

.github/actions/cache-db/action.yml

@@ -32,14 +32,16 @@ runs:
       shell: bash
     - name: Postgres Dump Backup
       if: steps.cache-db.outputs.cache-hit != 'true'
-      uses: tj-actions/pg-dump@v2.3
-      with:
-        database_url: ${{ inputs.DATABASE_URL }}
-        path: ${{ inputs.path }}
-        options: "-O"
+      run: |
+        mkdir -p $(dirname "${{ inputs.path }}")
+        docker run --rm --network host \
+          -v ${{ github.workspace }}:${{ github.workspace }} -w ${{ github.workspace }} \
+          postgres:18 pg_dump "${{ inputs.DATABASE_URL }}" -O -f ${{ inputs.path }}
+      shell: bash
     - name: Postgres Backup Restore
       if: steps.cache-db.outputs.cache-hit == 'true'
-      uses: tj-actions/pg-restore@v4.5
-      with:
-        database_url: ${{ inputs.DATABASE_URL }}
-        backup_file: ${{ inputs.path }}
+      run: |
+        docker run --rm -i --network host \
+          -v ${{ github.workspace }}:${{ github.workspace }} -w ${{ github.workspace }} \
+          postgres:18 psql "${{ inputs.DATABASE_URL }}" -f ${{ inputs.path }}
+      shell: bash