[.github/workflows/linux-Windows-macOS-sunOS.yml] Remove SunOS as runner is no longer available (logic still present for future work to add SunOS back)

Author: SamuelMarks

.github/workflows/linux-Windows-macOS-sunOS.yml

@@ -11,7 +11,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: [ubuntu-latest, windows-latest, macos-latest, macos-10.15]
+        os: [ubuntu-latest, windows-latest, macos-latest]
 
     name: ${{ matrix.os == 'macos-10.15' && 'SunOS' || matrix.os }}