add ui-toml test

Author: jonboh

tests/ui-toml/enum_variants_threshold0/clippy.toml

@@ -0,0 +1 @@
+enum-variant-name-threshold = 0

tests/ui-toml/enum_variants_threshold0/enum_variants_name_threshold.rs

@@ -0,0 +1,3 @@
+enum Actions {}
+
+fn main() {}