Prepare for branch renaming. (#367)

* Add `amd-staging` and `amd-mainline` to workflow
* Update links in documentation to use amd-mainline

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Signed-off-by: David Galiffi <David.Galiffi@amd.com>

docs/sphinx/_toc.yml.in

@@ -17,7 +17,7 @@ subtrees:
 
   - caption: Tutorials
     entries:
-    - url: https://github.com/ROCm/omnitrace/tree/main/examples
+    - url: https://github.com/ROCm/omnitrace/tree/amd-mainline/examples
       title: GitHub examples
     - file: tutorials/video-tutorials.rst
       title: Video tutorials