Add babel group to dependabot config

I didn't think to add this because we don't have babel dependencies
directly, but we recently had a few separate PRs to update babel
dependencies, because they are pulled in transitively and had some
security fixes. Adding this config will reduce the number of PRs we have
to deal with here and help all of the babel deps be updated together.

Author: lencioni

.github/dependabot.yml

@@ -7,6 +7,10 @@ updates:
     schedule:
       interval: daily
     groups:
+      babel:
+        patterns:
+          - '@babel/*'
+          - 'babel*'
       docusaurus:
         patterns:
           - '@docusaurus/*'