Add "Import assertions" to "javascript" group (web-platform-dx#3665)

Author: jugglinmike

features/import-assertions.yml

@@ -1,6 +1,7 @@
 name: Import assertions
 description: 'Module `import … assert { type: "json" }` and `import … assert { type: "css" }` JavaScript statements load JSON and CSS data.'
 spec: https://github.com/tc39/proposal-import-attributes/tree/abca60286360b47f9a6be25a28f489c2cb157beb
+group: javascript
 discouraged:
   reason: Import assertions are superseded by import attributes.
   removal_date: 2024-06-13