stdlib: Update the gem5 resources' version to "v22.1"

This is required to ensure the correct version of the resources are
obtained for this version of gem5.

Change-Id: If316081c776d510ec9a2f7ff9e077a1f837d2d2e
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/65915
Reviewed-by: Bobby Bruce <bbruce@ucdavis.edu>
Tested-by: kokoro <noreply+kokoro@google.com>
Maintainer: Bobby Bruce <bbruce@ucdavis.edu>
diff --git a/src/python/gem5/resources/downloader.py b/src/python/gem5/resources/downloader.py
index 1fda8d8..f619b97 100644
--- a/src/python/gem5/resources/downloader.py
+++ b/src/python/gem5/resources/downloader.py
@@ -55,7 +55,7 @@
     """
     Specifies the version of resources.json to obtain.
     """
-    return "develop"
+    return "22.1"
 
 
 def _get_resources_json_uri() -> str: