Add skip_import to PythonPackage and use it in py-nilearn (#32664)

* Add skip_import to PythonPackage and use it in py-nilearn

* Fix dependencies

lib/spack/spack/build_systems/python.py

@@ -138,12 +138,28 @@ def import_modules(self):
                     path.replace(root + os.sep, "", 1).replace(".py", "").replace("/", ".")
                 )
 
-        modules = [mod for mod in modules if re.match("[a-zA-Z0-9._]+$", mod)]
+        modules = [
+            mod
+            for mod in modules
+            if re.match("[a-zA-Z0-9._]+$", mod) and not any(map(mod.startswith, self.skip_modules))
+        ]
 
         tty.debug("Detected the following modules: {0}".format(modules))
 
         return modules
 
+    @property
+    def skip_modules(self):
+        """Names of modules that should be skipped when running tests.
+
+        These are a subset of import_modules. If a module has submodules,
+        they are skipped as well (meaning a.b is skipped if a is contained).
+
+        Returns:
+            list: list of strings of module names
+        """
+        return []
+
     @property
     def build_directory(self):
         """The root directory of the Python package.