fix(native): stop the eglInitialize flake in the render tests

[omartelo]

The native render tests skipped intermittently on CI with eglInitialize failed: 0x3001 (3 of the last 15 native runs, main included), and a skip fails the job.

Root cause

Each headless.NewWindow opens the default EGL display, which on Mesa's X11 platform is its own Xvfb connection, and Release closes it. That connection is the only client, so Xvfb regenerates the server every time a test window goes away: 63 to 66 server generations per go test ./... run, counted from the xkbcomp lines Xvfb logs on each reset. An eglInitialize that lands while the server is resetting gets EGL_BAD_ALLOC ... xcb_connect failed (EGL_LOG_LEVEL=debug), which Gio reports as 0x3001. All 19 failures in the measurement loop were this one error.

Fix

Start Xvfb with -noreset (the screen argument stays the runner's xvfb-run default, -screen 0 1280x1024x24). No test, skip or guard changed.

Measurement

Temporary loop on ubuntu-latest, full xvfb-run go test -v ./... per iteration, counting no headless GPU:

variant	runs	runs with a skip	skips	server generations per run
baseline	60 + 80	11 + 17 (20%)	14 + 19	63 to 66
-noreset	80	0	0	1

EGL_PLATFORM=surfaceless also went 0/60, but it sidesteps X instead of fixing the reset. The loop workflow is removed from this branch.