add: build group property in gen-doc task

Signed-off-by: Shunsuke Kimura <[email protected]>

Author: kimushun1101

.vscode/tasks.json

@@ -5,7 +5,11 @@
       "label": "generate-docs",
       "type": "shell",
       "command": "cargo test --package typst-docs --lib -- tests::test_docs --exact --nocapture && python3 ./gen.py && echo reload or open http://localhost:8000",
-      "problemMatcher": []
+      "problemMatcher": [],
+      "group": {
+        "kind": "build",
+        "isDefault": true
+      },
     },
     {
       "label": "textlint-md",