fix(ci): update first-interaction input names for v3

The `actions/first-interaction@v3` renamed inputs from kebab-case to
snake_case (`repo_token`, `issue_message`, `pr_message`).

Co-Authored-By: Claude <noreply@anthropic.com>

Author: zrosenbauer

.github/workflows/welcome.yaml

@@ -23,10 +23,10 @@ jobs:
     steps:
       - uses: actions/first-interaction@v3
         with:
-          repo-token: ${{ secrets.GITHUB_TOKEN }}
-          issue-message: >
+          repo_token: ${{ secrets.GITHUB_TOKEN }}
+          issue_message: >
             Thanks for opening your first issue! The Joggr team will review
             this shortly.
-          pr-message: >
+          pr_message: >
             Thanks for your first pull request! The Joggr team will review
             this shortly.