modules: don't assume macOS is only desktop GL in FindMagnum.

The GLES3 macOS CI build was added exactly because of this, but this
wasn't caught. Only now when I added a GLES3 macOS build for the
integration repos.

modules/FindMagnum.cmake

@@ -388,8 +388,7 @@ if(CORRADE_TARGET_EMSCRIPTEN)
 endif()
 if(CORRADE_TARGET_IOS)
     list(APPEND _MAGNUM_LIBRARY_COMPONENTS WindowlessIosApplication)
-endif()
+elseif(CORRADE_TARGET_APPLE AND NOT MAGNUM_TARGET_GLES)
-if(CORRADE_TARGET_APPLE AND NOT CORRADE_TARGET_IOS)
     list(APPEND _MAGNUM_LIBRARY_COMPONENTS WindowlessCglApplication CglContext)
 endif()
 if(CORRADE_TARGET_UNIX AND NOT CORRADE_TARGET_APPLE)
@@ -431,7 +430,7 @@ if(MAGNUM_TARGET_HEADLESS OR CORRADE_TARGET_EMSCRIPTEN OR CORRADE_TARGET_ANDROID
     list(APPEND _MAGNUM_OpenGLTester_DEPENDENCIES WindowlessEglApplication)
 elseif(CORRADE_TARGET_IOS)
     list(APPEND _MAGNUM_OpenGLTester_DEPENDENCIES WindowlessIosApplication)
-elseif(CORRADE_TARGET_APPLE)
+elseif(CORRADE_TARGET_APPLE AND NOT MAGNUM_TARGET_GLES)
     list(APPEND _MAGNUM_OpenGLTester_DEPENDENCIES WindowlessCglApplication)
 elseif(CORRADE_TARGET_UNIX)
     if(MAGNUM_TARGET_GLES AND NOT MAGNUM_TARGET_DESKTOP_GLES)