Rename self-hosted Mac CI workflow file for consistency

Call this file consistently with the other CI files and also ignore all
of the other files in each workflow to avoid unnecessary rebuilds.

Finally, remove a leftover mention of Travis file which doesn't exist
any longer.

.github/workflows/ci.yml

@@ -6,7 +6,7 @@ on:
     branches:
       - master
     paths-ignore:
-      - '.github/workflows/MacS-M1-make.yml'
+      - '.github/workflows/ci_mac_selfhosted.yml'
       - '.github/workflows/ci_cmake.yml'
       - '.github/workflows/ci_msw_cross.yml'
       - 'build/tools/appveyor*.bat'
@@ -24,7 +24,7 @@ on:
     branches:
       - master
     paths-ignore:
-      - '.github/workflows/MacS-M1-make.yml'
+      - '.github/workflows/ci_mac_selfhosted.yml'
       - '.github/workflows/ci_cmake.yml'
       - '.github/workflows/ci_msw_cross.yml'
       - 'build/tools/appveyor*.bat'