test: reduce integration tests concurrency to 8, e2e max paralle to 2

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: vdusek

.github/workflows/_tests.yaml

@@ -36,7 +36,7 @@ jobs:
     runs-on: ${{ matrix.os }}
 
     env:
-      TESTS_CONCURRENCY: "16"
+      TESTS_CONCURRENCY: "8"
 
     steps:
       - name: Checkout repository
@@ -85,11 +85,15 @@ jobs:
         (github.event_name == 'push' && github.ref == 'refs/heads/master')
       }}
 
+    # E2E tests build and run Actors on the platform. The combination of max-parallel 2 with 16 pytest
+    # workers and a global concurrency group is a compromise between stability and performance - it keeps
+    # the platform's resource usage in check while still allowing reasonable test throughput.
+    concurrency:
+      group: e2e-tests
+      cancel-in-progress: false
+
     strategy:
-      # E2E tests build and run Actors on the platform. Limit parallel workflows to 1 to avoid exceeding
-      # the platform's memory limits. A single workflow with 16 pytest workers provides good test
-      # parallelization while staying within platform constraints.
-      max-parallel: 1
+      max-parallel: 2
       matrix:
         os: ["ubuntu-latest"]
         python-version: ["3.10", "3.14"]