Pass testOnlyPath in environment instead of command line.

It's typically a very very long string, which made Windows angry.

Author: prdoyle

build-tools-internal/src/main/java/org/elasticsearch/gradle/internal/ElasticsearchTestBasePlugin.java

@@ -182,7 +182,7 @@ public void execute(Task t) {
                 FileCollection mainRuntime = mainSourceSet.getRuntimeClasspath();
                 FileCollection testRuntime = testSourceSet.getRuntimeClasspath();
                 FileCollection testOnlyFiles = testRuntime.minus(mainRuntime);
-                nonInputProperties.systemProperty("es.entitlement.testOnlyPath", testOnlyFiles::getAsPath);
+                test.environment("es.entitlement.testOnlyPath", testOnlyFiles.getAsPath());
             }
 
             test.systemProperties(getProviderFactory().systemPropertiesPrefixedBy("tests.").get());

test/framework/src/main/java/org/elasticsearch/entitlement/bootstrap/TestEntitlementBootstrap.java

@@ -122,12 +122,12 @@ private static TestPolicyManager createPolicyManager(PathLookup pathLookup) thro
 
         FilesEntitlementsValidation.validate(pluginPolicies, pathLookup);
 
-        String testOnlyPathProperty = System.getProperty("es.entitlement.testOnlyPath");
+        String testOnlyPathString = System.getenv("es.entitlement.testOnlyPath");
         Set<String> testOnlyClassPath;
-        if (testOnlyPathProperty == null) {
+        if (testOnlyPathString == null) {
             testOnlyClassPath = Set.of();
         } else {
-            testOnlyClassPath = Arrays.stream(testOnlyPathProperty.split(":")).collect(toCollection(TreeSet::new));
+            testOnlyClassPath = Arrays.stream(testOnlyPathString.split(":")).collect(toCollection(TreeSet::new));
         }
 
         return new TestPolicyManager(