[GLib] Test file name should be the same name as target class

[asfimport]

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

_{Note: This issue was originally created as ARROW-1228. Please see the migration documentation for further details.}

[asfimport]

Uwe Korn / @xhochy:
Issue resolved by pull request 857
#857