infra: Fix dependabot config file.

 * The yaml file was a dependabot config file, not a GitHub actions
   workflow config file.

Signed-off-by: Tim 'mithro' Ansell <me@mith.ro>
diff --git a/.github/workflows/dependabot-gha.yml b/.github/dependabot.yml
similarity index 100%
rename from .github/workflows/dependabot-gha.yml
rename to .github/dependabot.yml