[dependabot] Ignore typescript and prettier (#31665)

- Updated manually to align with microsoft/typespec repo

.github/dependabot.yml

@@ -9,6 +9,9 @@ updates:
   ignore:
   # Updated manually to align with minimum supported Node version
   - dependency-name: "@types/node"
+  # Updated manually to align with repo microsoft/typespec
+  - dependency-name: "typescript"
+  - dependency-name: "prettier"
   # minimatch@9 is the last version to support Node 18
   - dependency-name: "minimatch"
     versions: [ ">= 10.0.0"]