[ci] Do not run mac-beta builds on workflow dispatch triggers

to avoid loading the CI upon releasing.

Author: dpiparo

.github/workflows/root-ci.yml

@@ -106,6 +106,7 @@ jobs:
             arch: ARM64
             overrides: ["CMAKE_CXX_STANDARD=20"]
           - platform: mac-beta
+            is_special: true
             arch: ARM64
             overrides: ["CMAKE_CXX_STANDARD=20"]
 
@@ -174,7 +175,7 @@ jobs:
                     --platform        ${{ matrix.platform }}"
 
       - name: Workflow dispatch
-        if:   github.event_name == 'workflow_dispatch'
+        if: ${{ github.event_name == 'workflow_dispatch' && !matrix.is_special }}
         run: ".github/workflows/root-ci-config/build_root.py
                     --buildtype      ${{ inputs.buildtype }}
                     --platform       ${{ matrix.platform }}