Bug 1762128 - bump the cache name for decision images to stop interfering with...

Bug 1762128 - bump the cache name for decision images to stop interfering with other trees. r=releng-reviewers,ahal a=release

hg 4.8 (e.g. from the v3.0.1 decision image) seems to choke on cached repos
created with 5.8 (from v4.0.0).

Differential Revision: https://phabricator.services.mozilla.com/D142455

.taskcluster.yml

@@ -214,7 +214,7 @@ tasks:
                                 ACTION_CALLBACK: '${action.cb_name}'
 
                   cache:
-                      "${trustDomain}-level-${repository.level}-checkouts-sparse-v2": /builds/worker/checkouts
+                      "${trustDomain}-level-${repository.level}-checkouts-sparse-v3": /builds/worker/checkouts
 
                   features:
                       taskclusterProxy: true