build(python): gridfire uses fourdst wheel in python mode

tests/meson.build

@@ -4,5 +4,9 @@
 #gtest_nomain_dep = dependency('gtest', main: false, required : true)
 
 # Subdirectories for unit and integration tests
-subdir('graphnet_sandbox')
-subdir('extern')
+if get_option('build_tests') and not get_option('build_python')
+    subdir('graphnet_sandbox')
+    subdir('extern')
+else
+    message('Tests disabled by build options! To enable them build with build_tests = true and build_python=false')
+endif