set JAVA_HOME via workflow

Author: shahmishal

.github/workflows/pull_request.yml

@@ -10,4 +10,6 @@ jobs:
         uses: swiftlang/github-workflows/.github/workflows/swift_package_test.yml@main
         with:
           exclude_swift_versions: "[{\"swift_version\": \"5.8\"}]"
-          pre_build_command: "apt-get update -y -q && apt-get install -y -q openjdk-21-jdk && export JAVA_HOME=\"/usr/lib/jvm/java-21-openjdk-amd64\""
+          pre_build_command: "apt-get update -y -q && apt-get install -y -q openjdk-21-jdk"
+          env_vars: |
+            JAVA_HOME="/usr/lib/jvm/java-21-openjdk-amd64"