chore: rename issue template contact link to match its destination (#1926)

The "GitHub Community Support" name came from the config.yml example in
GitHub's documentation, where it pointed at the official community forum
(github.com/orgs/community/discussions). #1338 repointed the URL at this
repository's own Discussions but left the name unchanged, so the issue
chooser advertised GitHub's official support while linking to the
project's Discussions.