glamor: require GLES 2.0 on GL ES CI

This will help us to catch GLES 2.0 only bugs. Anyway, for now all relevant GLES2 users of Glamor using GLES 2.0 due to inability of run GL 2.1.

There are test failures, which is fixed by !1158 (merged).

Fixes #818 (closed)

CC: @ajax @ofourdan @anholt @daenzer

Signed-off-by: Konstantin ria.freelander@gmail.com