Revert "Use RMM main (new branching strategy)" (#869)

This reverts commit fde70e1.

Authors:
  - Robert Maynard (https://github.com/robertmaynard)

Approvers:
  - Jake Awe (https://github.com/AyodeAwe)
  - Bradley Dice (https://github.com/bdice)

URL: #869

Author: robertmaynard

rapids-cmake/cpm/versions.json

@@ -72,7 +72,7 @@
     "rmm": {
       "version": "${rapids-cmake-version}",
       "git_url": "https://github.com/rapidsai/rmm.git",
-      "git_tag": "main"
+      "git_tag": "branch-${version}"
     },
     "spdlog": {
       "version": "1.14.1",