CI: Fix ARM64 install script exit code handling

The run-on-arch-action fails with exit code 100 even when packages install
successfully because apt update returns 100 for dep11 metadata failures.

The install script properly handles dep11 failures (retries for critical
indices, ignores dep11, verifies package installation), but doesn't
explicitly exit 0 at the end. The action captures the last command's exit
code, which is from the apt update attempt that had dep11 failures.

Fix: Add explicit "exit 0" at end of install script after verifying all
critical packages are installed. This ensures the action sees success when
packages are actually installed correctly, regardless of benign dep11
metadata sync issues.

Fixes: host-arm64 "exit code 100" despite successful package installation

Author: jserv

.github/workflows/main.yml

@@ -415,6 +415,9 @@ jobs:
           fi
 
           echo "✓ All critical build tools installed successfully"
+
+          # Explicitly exit with success (install script may have non-zero from apt update dep11)
+          exit 0
         # FIXME: gcc build fails on Aarch64/Linux hosts
         env: |
           CC: clang-18