Use processIsolation for SigstoreSignFilesTask to avoid OutOfMemory: MetaSpace

see gradle/gradle#18313

Signed-off-by: Vladimir Sitnikov <sitnikov.vladimir@gmail.com>

Author: vlsi

sigstore-gradle/sigstore-gradle-sign-base-plugin/src/main/kotlin/dev/sigstore/sign/tasks/SigstoreSignFilesTask.kt

@@ -121,7 +121,12 @@ abstract class SigstoreSignFilesTask : DefaultTask() {
     @TaskAction
     protected fun sign() {
         workerExecutor
-            .classLoaderIsolation { classpath.from(sigstoreClientClasspath) }
+            .processIsolation {
+                classpath.from(sigstoreClientClasspath)
+                forkOptions {
+                    environment(System.getenv())
+                }
+            }
             .run {
                 for (signature in signatures) {
                     submit(SignWorkAction::class.java) {