Fixed code smell 'Define a constant instead of duplicating this literal' reported by SonarQube.

web/pgadmin/tools/restore/__init__.py

@@ -23,6 +23,7 @@ from pgadmin.utils.ajax import make_json_response, bad_request
 
 from config import PG_DEFAULT_DRIVER
 from pgadmin.model import Server
+from pgadmin.utils.constants import MIMETYPE_APP_JS
 
 # set template path for sql scripts
 MODULE_NAME = 'restore'
@@ -151,7 +152,7 @@ def script():
             "restore/js/restore.js", _=_
         ),
         status=200,
-        mimetype="application/javascript"
+        mimetype=MIMETYPE_APP_JS
     )