ci: consolidate platform pipelines and test prerequisites on macOS support

MeetingAssistant.Tests/TaskbarIconTests.cs

@@ -177,15 +177,10 @@ public sealed class TaskbarIconTests
             MeetingTaskbarExitPolicy.RequiresConfirmation(state));
     }
 
-    [Fact]
+    [WindowsFact("System.Drawing bitmap rendering")]
     [SupportedOSPlatform("windows")]
     public void TaskbarIconGlyphsAreVisuallyCentered()
     {
-        if (!OperatingSystem.IsWindows())
-        {
-            return;
-        }
-
         foreach (var state in new[]
         {
             RecordingProcessState.Idle,