Add default severity level to emotion rule

Author: joephela

.changeset/sour-pots-know.md

@@ -0,0 +1,5 @@
+---
+'eslint-config-widen-emotion': minor
+---
+
+Add a default severity level.

packages/eslint-config-widen-emotion/src/index.ts

@@ -2,6 +2,6 @@ import noConditionalCssProp from './rules/no-conditional-css-prop.js'
 
 export default {
   rules: {
-    'no-conditional-css-prop': noConditionalCssProp,
+    'no-conditional-css-prop': ['warn', noConditionalCssProp],
   },
 }