[Conan] use Ninja by default

CI/conan/macos-arm

@@ -9,3 +9,5 @@ build_type=Release
 [options]
 [build_requires]
 [env]
+[conf]
+tools.cmake.cmaketoolchain:generator = Ninja

CI/conan/macos-intel

@@ -9,3 +9,5 @@ build_type=Release
 [options]
 [build_requires]
 [env]
+[conf]
+tools.cmake.cmaketoolchain:generator = Ninja