Use RuntimeError instead of ValueError when the retrieval of default modules fails

This will result in the error actually being in the state reason
of the failed module build instead of "An unknown error occurred
while validating the modulemd".

module_build_service/scheduler/default_modules.py

@@ -121,7 +121,7 @@ def _get_default_modules(stream, default_modules_scm_url):
     :return: a dictionary where the keys are default module names and the values are default module
         streams
     :rtype: dict
-    :raise ValueError: if no default modules can be retrieved for that stream
+    :raise RuntimeError: if no default modules can be retrieved for that stream
     """
     scm_obj = scm.SCM(default_modules_scm_url)
     temp_dir = tempfile.mkdtemp()
@@ -167,7 +167,7 @@ def _get_default_modules(stream, default_modules_scm_url):
     except:  # noqa: E722
         msg = "Failed to retrieve the default modules"
         log.exception(msg)
-        raise ValueError(msg)
+        raise RuntimeError(msg)
     finally:
         shutil.rmtree(temp_dir)
 

tests/test_scheduler/test_default_modules.py

@@ -183,7 +183,7 @@ def test_get_default_modules_invalid_branch(
     else:
         mock_get_rawhide.return_value = "something_else"
 
-    with pytest.raises(ValueError, match="Failed to retrieve the default modules"):
+    with pytest.raises(RuntimeError, match="Failed to retrieve the default modules"):
         default_modules._get_default_modules("f32", conf.default_modules_scm_url)
 
     mock_mmd_new.assert_not_called()