i#6678 Rename aarchxx workflows, part 2: Rename native ci-aarchxx yml…

… file

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 part one (#xyz) we renamed the cross ci-aarchxx to ci-aarchxx-cross,
in the workflow name and yml file name.
In this part two we 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.

Fixes #6678