chore: raise ee-test JVM heap to 8G to avoid OOM under Spring Boot 4

The ee-test suite runs all tests in one JVM and caches up to 32 Spring test contexts
(spring.test.context.cache default). Spring Boot 4 contexts are heavier, so 32 cached
contexts intermittently exhaust the 4G test heap, throwing OutOfMemoryError during a
later context load (surfaces as flaky QaCheck* / ee-test failures). The GitHub runner has
~16G, so raising the forked test JVM heap to 8G gives the context cache room without
risking OS memory pressure (only this JVM plus the gradle process and Postgres/Redis run).

Author: bdshadow

ee/backend/tests/build.gradle

@@ -29,7 +29,7 @@ allOpen {
 
 tasks.named('test', Test) {
     useJUnitPlatform()
-    maxHeapSize = "4096m"
+    maxHeapSize = "8192m"
     rootProject.setTestRetry(it)
 }