Update PR Workflow (rapidsai#1174)

Because of the changes in rapidsai/shared-workflows#24, we need to update the `rmm` PR workflow accordingly.

Similar to rapidsai/cudf#12296.

Author: ajschmidt8

.github/workflows/pr.yaml

@@ -11,6 +11,12 @@ concurrency:
 
 jobs:
   pr-builder:
+    needs:
+      - checks
+      - conda-cpp-build
+      - conda-cpp-tests
+      - conda-python-build
+      - conda-python-tests
     secrets: inherit
     uses: rapidsai/shared-action-workflows/.github/workflows/pr-builder.yaml@main
   checks: