i#6678 Rename aarchxx workflows, part 1: ci-aarchxx -> ci-aarchxx-cross

There are currently two workflows name "ci-aarchxx" which is confusing.
The ci-aarch64-native workflow was renamed to ci-aarchxx in #6549 with
the goal of being consistent with other architecture workflows.
However, this introduced the ambiguous "ci-aarchxx" naming.

Fix this by renaming ci-aarchxx.yml -> ci-aarchxx-cross.yml, and
renaming ci-aarch64-native.yml -> ci-aarchxx.yml.
Furthermore, rename the aarchxx "cross" workflow to ci-aarchxx-cross.

This accomplishes three things:
1) Naming is consistent with the other workflow files: native workflows
are named "ci-$ARCH" and live in file "ci-$ARCH.yml".
2) All workflows have unique names.
3) The yml file and workflow have the same name.

In this part one we rename the cross ci-aarchxx to ci-aarchxx-cross,
in the workflow name and yml file name.
In part two to follow (#xyz) we will leave the workflow name alone, but
still rename the file from ci-aarch64-native.yml to ci-aarchxx.yml.
The renaming is split into two to better preserve the history:
Git can track file renamings, but not when the original file is also
replaced with something different.

Issue #6678

.github/workflows/ci-aarchxx.yml → .github/workflows/ci-aarchxx-cross.yml

@@ -30,7 +30,7 @@
 
 # Github Actions workflow for AArchXX Continuous Integration testing.
 
-name: ci-aarchxx
+name: ci-aarchxx-cross
 on:
   # Run on pushes to master and on pull request changes, including from a
   # forked repo with no "push" trigger, while avoiding duplicate triggers.