Target new Win10 Intel driver on stable

Adds driver 26.20.100.8141 as a target for both HD 630 and UHD 630 GPUs
for stable GPU testerse, as the driver has been qualified and the
upgrade will be rolled out in the near future.

Bug: 1053803
Change-Id: I6de2c27bcedd71b05829c7c52e3aea754c1bdc23
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2258679
Auto-Submit: Brian Sheedy <bsheedy@chromium.org>
Reviewed-by: Yuly Novikov <ynovikov@chromium.org>
Commit-Queue: Brian Sheedy <bsheedy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#781916}

testing/buildbot/mixins.pyl

@@ -738,8 +738,8 @@
       # to trigger tests on multiple configurations.
       'dimension_sets': [
         {
-          'gpu': '8086:5912-24.20.100.6286',
-          'os': 'Windows-10-17134',
+          'gpu': '8086:5912-24.20.100.6286|8086:5912-26.20.100.8141',
+          'os': 'Windows-10-17134|Windows-10-18363',
           'pool': 'chromium.tests.gpu',
         },
       ],
@@ -766,7 +766,7 @@
   'win10_intel_hd_630_stable': {
     'swarming': {
       'dimensions': {
-        'gpu': '8086:5912-24.20.100.6286',
+        'gpu': '8086:5912-24.20.100.6286|8086:5912-26.20.100.8141|8086:3e92-26.20.100.8141',
         'os': 'Windows-10',
         'pool': 'chromium.tests.gpu',
       },