Update Win10 Experimental Intel driver

Updates the driver version targeted by
Win10 FYI x64 Exp Release (Intel HD 630) from 24.20.100.6286 (stable) to
26.20.100.6912.

TBR=kbr@chromium.org

Bug: 916832
Change-Id: I048e84b5aacbb0283cb84a487e75fcd5321d88f7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1764759Reviewed-by: Brian Sheedy <bsheedy@chromium.org>
Reviewed-by: Kenneth Russell <kbr@chromium.org>
Commit-Queue: Brian Sheedy <bsheedy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#689574}

testing/buildbot/mixins.pyl

@@ -589,7 +589,7 @@
     # Currently same as stable version.
     'swarming': {
       'dimensions': {
-        'gpu': '8086:5912-24.20.100.6286',
+        'gpu': '8086:5912-26.20.100.6912',
         'os': 'Windows-10',
         'pool': 'Chrome-GPU',
       },