glsl/float64: Bump #version to 400

glsl/float64: Bump #version to 400

An earlier commit tried to make this shader compatible with GLSL 3.30,
but it requires, GL_ARB_gpu_shader_int64, which requires GLSL 4.00 and
GL 4.0 according to the extension spec.  So we were failing to enable
the required extension, breaking compilation of this shader.

The original intention of that patch was to get this working on zink,
which at the time only supported GL 3.3.  But now it supports later
OpenGL versions, so we don't need to do this any longer.  Rather than
revert the patch and raise the version all the way back to 430, just
bump it to the require 400 at Ian Romanick's suggestion.

Fixes: 4d47b22bf00 ("glsl/float64: make this compatible with glsl 330")
Closes: https://gitlab.freedesktop.org/mesa/mesa/-/issues/3991
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/9351>