Fix unclosed files in standalone tests

Author: msimacek

graalpython/com.oracle.graal.python.test/src/tests/standalone/test_gradle_plugin.py

@@ -130,7 +130,8 @@ def check_gradle_generated_app(self):
 
             # import struct from python file triggers extract of native extension files in VirtualFileSystem
             hello_src = os.path.join(target_dir, "src", "main", "resources", "org.graalvm.python.vfs", "src", "hello.py")
-            contents = open(hello_src, 'r').read()
+            with open(hello_src) as f:
+                contents = f.read()
             with open(hello_src, 'w') as f:
                 f.write("import struct\n" + contents)
 

graalpython/com.oracle.graal.python.test/src/tests/standalone/test_maven_plugin.py

@@ -111,7 +111,8 @@ def test_generated_app(self):
 
             # import struct from python file triggers extract of native extension files in VirtualFileSystem
             hello_src = os.path.join(target_dir, "src", "main", "resources", "org.graalvm.python.vfs", "src", "hello.py")
-            contents = open(hello_src, 'r').read()
+            with open(hello_src) as f:
+                contents = f.read()
             with open(hello_src, 'w') as f:
                 f.write("import struct\n" + contents)