Revert "Increase java heap size to 6GB"

This reverts commit 6156639.

Author: ghostbuster91

.github/workflows/main.yaml

@@ -11,7 +11,7 @@ jobs:
   build:
     runs-on: ubuntu-20.04
     env:
-      JAVA_OPTS: -Xmx6G
+      JAVA_OPTS: -Xmx4G
     steps:
       - uses: actions/checkout@v2
       - uses: coursier/[email protected]
@@ -29,7 +29,7 @@ jobs:
     needs: [build]
     runs-on: ubuntu-20.04
     env:
-      JAVA_OPTS: -Xmx6G
+      JAVA_OPTS: -Xmx4G
     steps:
       - uses: actions/[email protected]
         with: