GL_SRG8_ALPHA8 also supported in OpenGL ES 3.0+

GL_SRG8_ALPHA8 also supported in OpenGL ES 3.0+

dEQP-GLES2.functional.fbo.completeness.renderable.texture.color0.srgb8_alpha8
assumes that using GL_SRGB8_ALPHA8 in GLES2 should fail unless proper
extensions are supported.

But the OpenGL ES context created can be either 2.0 or an upper version,
and upper versions (3.0+) supports this format without extensions.

Thus, if OpenGL ES 3.0+ context is returned, this test should assume
that rendering is possible.

This is an extension of fix done in Change-ID
Ibb95736959ff9d5b0ff972ccf3983abc98795be3.

Affectd tests:
dEQP-GLES2.functional.fbo.completeness.renderable.texture.color0.srgb8_alpha8

Components: OpenGL

VK-GL-CTS issue: 1137

Change-Id: I733a8595b1eba7756787cde4a6bca2391dc345d7
(cherry picked from commit dd951adf61b3b6ad6cdab92b26b00c6931235681)