CI: Run CI and JS artifact build on self-hosted runner

The GitHub-provided runner frequently times out and is plain slow most
of the time. And since Blacksmith does not yet offer macOS runners,
let's use our self-hosted runner that is currently idle most of the time
(when it's not running JS benchmarks).

.github/workflows/ci.yml

@@ -34,7 +34,7 @@ jobs:
             build_preset: 'Sanitizer_CI'
             toolchain: 'Clang'
             clang_plugins: false
-            runner_labels: '["macos-15"]'
+            runner_labels: '["macos-15", "self-hosted"]'
 
           - os_name: 'Linux'
             arch: 'x86_64'

.github/workflows/js-artifacts.yml

@@ -25,7 +25,7 @@ jobs:
           - os_name: 'macOS'
             arch: 'arm64'
             package_type: 'macOS-arm64'
-            runner_labels: '["macos-15"]'
+            runner_labels: '["macos-15", "self-hosted"]'
 
     steps:
       - name: Checkout LadybirdBrowser/ladybird