Fix Typo [ci skip] (#13742)

I'm going over this today in an onboarding tech dive and I'm apparently more OCD than I thought.

frontend/src/metabase-lib/lib/metadata/Database.js

@@ -35,7 +35,7 @@ export default class Database extends Base {
     return this.name;
   }
 
-  // SCEMAS
+  // SCHEMAS
 
   schema(schemaName: ?SchemaName) {
     return this.metadata.schema(generateSchemaId(this.id, schemaName));