fix(ci): use the underscore input names of actions/first-interaction

The action declares issue_message, pr_message and repo_token. With the
hyphenated spelling none of them arrive and the workflow fails on the
first outside contribution: 'Input required and not supplied:
issue_message'. Only the three keys change, the greeting text stays.

Author: lukisch

.github/workflows/welcome.yml

@@ -16,16 +16,16 @@ jobs:
     steps:
       - uses: actions/first-interaction@v3
         with:
-          repo-token: ${{ secrets.GITHUB_TOKEN }}
-          issue-message: |
+          repo_token: ${{ secrets.GITHUB_TOKEN }}
+          issue_message: |
             Welcome! 👋 Thanks for opening your first issue in this repository.
 
             We'll review it as soon as possible. In the meantime:
             - Check if there's a similar issue already open
             - Add as much detail as possible (steps to reproduce, expected behavior, environment)
 
             If you'd like to contribute a fix, PRs are always welcome!
-          pr-message: |
+          pr_message: |
             Welcome! 👋 Thanks for your first pull request in this repository.
 
             A maintainer will review it soon. Please make sure: