fix: Reduce TEST_CONCURRENCY from 8 to 4 to prevent OOM kills

Each Next.js test spawns a dev/prod server with webpack compilation,
using ~1-2 GB RAM per server. With TEST_CONCURRENCY=8 and 4-core
runners (16 GB RAM), 8 concurrent servers could use 8-16+ GB RAM,
triggering the Linux OOM killer and causing tests to be "killed".

Reducing to 4 concurrent tests (matching core count) should keep
memory usage within bounds while still utilizing available parallelism.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: celicoo

.github/workflows/build_reusable.yml

@@ -52,8 +52,11 @@ env:
   TURBO_VERSION: 2.5.5
   NODE_LTS_VERSION: 20.9.0
   # run-tests.js reads `TEST_CONCURRENCY` if no explicit `--concurrency` or `-c`
-  # argument is provided
-  TEST_CONCURRENCY: 8
+  # argument is provided.
+  # NOTE: Each Next.js test spawns a dev/prod server with webpack compilation,
+  # using ~1-2 GB RAM per server. 4-core runners have 16 GB RAM, so we limit to
+  # 4 concurrent tests to prevent OOM (Out of Memory) kills.
+  TEST_CONCURRENCY: 4
 
   NEXT_TELEMETRY_DISABLED: 1
   NEXT_JUNIT_TEST_REPORT: 'true'

.github/workflows/build_reusable_bun.yml

@@ -42,8 +42,11 @@ on:
 
 env:
   # run-tests.js reads `TEST_CONCURRENCY` if no explicit `--concurrency` or `-c`
-  # argument is provided
-  TEST_CONCURRENCY: 8
+  # argument is provided.
+  # NOTE: Each Next.js test spawns a dev/prod server with webpack compilation,
+  # using ~1-2 GB RAM per server. 4-core runners have 16 GB RAM, so we limit to
+  # 4 concurrent tests to prevent OOM (Out of Memory) kills.
+  TEST_CONCURRENCY: 4
 
   NEXT_TELEMETRY_DISABLED: 1
   NEXT_JUNIT_TEST_REPORT: 'true'