use prettier 3.1.0 in workflow

In 4f173ba I bumped the prettier version to 3.1. Whatever version we are using for the project should be the same as the workflow runs with (as we established in e-mission#1117)

.github/workflows/prettier.yml

@@ -7,6 +7,6 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v2
-      - run: npx prettier@3.0.3 --check www
+      - run: npx prettier@3.1.0 --check www