[GLib][CI] Unpin gobject-introspection gem

[asfimport]

Reporter: Kouhei Sutou / @kou
Assignee: Kouhei Sutou / @kou

PRs and other links:

• GitHub Pull Request #5572

_{Note: This issue was originally created as ARROW-6777. Please see the migration documentation for further details.}

[asfimport]

Kouhei Sutou / @kou:
Issue resolved by pull request 5572
#5572