Rename Mac clangd to Linux mac_clangd (#51785)

Further work towards flutter/flutter#141641.

Author: matanlurey

.ci.yaml

@@ -367,7 +367,7 @@ targets:
     drone_dimensions:
       - os=Mac-13
 
-  - name: Mac clangd
+  - name: Linux mac_clangd
     bringup: true
     recipe: engine_v2/engine_v2
     # Avoid using a Mac orchestrator to save ~5 minutes of Mac host time.