ci(apt): gate apt mirror swap on runs-on at the workflow level

Add 'if: startsWith(runner.name, "runs-on--")' to the mirror swap step
in both workflows so fork users can see at a glance that the step only
fires on runs-on runners and is a no-op on standard GitHub-hosted
runners. The script keeps its internal RUNS_ON_AWS_REGION check as
defense in depth for callers outside these workflows.

Signed-off-by: Ramon Roche <mrpollo@gmail.com>

.github/workflows/build_deb_package.yml

@@ -99,6 +99,7 @@ jobs:
           fetch-tags: true
 
       - name: Use AWS regional apt mirror
+        if: startsWith(runner.name, 'runs-on--')
         run: ./Tools/ci/use_aws_apt_mirror.sh
 
       - name: Cache apt packages

.github/workflows/compile_ubuntu.yml

@@ -50,6 +50,7 @@ jobs:
       - uses: actions/checkout@v4
 
       - name: Use AWS regional apt mirror
+        if: startsWith(runner.name, 'runs-on--')
         run: ./Tools/ci/use_aws_apt_mirror.sh
 
       - name: Install Deps, Build, and Make Quick Check