Add libglvnd-gles to the Firefox group (rhbz#1948010, fedora-kde/SIG#55)
Firefox's WebRender backend requires GLES to function, but the package
does not currently depend on it. In order to avoid being blocked on
the package being updated, the Firefox group will now include the
package.
Reference: https://bugzilla.redhat.com/1948010
Reference: https://pagure.io/fedora-kde/SIG/issue/55
Signed-off-by: Neal Gompa <ngompa13@gmail.com>