chore: Increase frontend unit test matrix to four shards (#39302)

Co-authored-by: n8n-cat-bot[bot] <n8n-cat-bot[bot]@users.noreply.github.com>

.github/workflows/test-unit-reusable.yml

@@ -299,12 +299,12 @@ jobs:
           files: ./packages/**/coverage/lcov.info
 
   unit-test-frontend:
-    name: Frontend (${{ matrix.shard }}/2)
+    name: Frontend (${{ matrix.shard }}/4)
     runs-on: ${{ vars.RUNNER_PROVIDER == 'github' && 'ubuntu-latest' || 'blacksmith-4vcpu-ubuntu-2204' }}
     strategy:
       fail-fast: false
       matrix:
-        shard: [1, 2]
+        shard: [1, 2, 3, 4]
     env:
       COVERAGE_ENABLED: ${{ inputs.collectCoverage }}
       AFFECTED_PACKAGES: ${{ inputs.affectedPackages }}
@@ -320,9 +320,9 @@ jobs:
           node-version: ${{ inputs.nodeVersion }}
 
       - name: Test
-        run: pnpm test:ci:frontend:changed --summarize -- --shard=${{ matrix.shard }}/2
+        run: pnpm test:ci:frontend:changed --summarize -- --shard=${{ matrix.shard }}/4
         env:
-          VITEST_SHARD: ${{ matrix.shard }}/2
+          VITEST_SHARD: ${{ matrix.shard }}/4
 
       - name: Send Test Stats
         if: ${{ !cancelled() }}