Re-add Linux to GpuPersistentCache fieldtrial testing.

The flakiness experienced on the Linux perf testers was bot specific.
The disk cache has been disabled on these bots for now.

Bug: 467161542
Bug: 399642827
Change-Id: Ia03816ad9806593fce3ddbadacd9d9c6dad77360
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/7525476
Reviewed-by: Kyle Charbonneau <kylechar@chromium.org>
Commit-Queue: Geoff Lang <geofflang@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1579508}
NOKEYCHECK=True
GitOrigin-RevId: 782235cc9a588d6ab557a7826372c38e7af70224