Double sharding of windows layout tests.

Per analysis in
https://docs.google.com/document/d/13KlGXF262SjyzHKTKSEu2LsQwqouDKurR1-HV9gxN9I/edit?ts=5db9f5dd#heading=h.4d6g0bxv5tz5

it should be possible to double sharding with a modreate increase in bot
capacity. The capacity increase was made in:

https://chrome-internal-review.googlesource.com/c/infradata/config/+/2098798

Bug: 1021179
Change-Id: I012ec294d5ba84a80c7480836937e46ec1518a27
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1900390Reviewed-by: Erik Chen <erikchen@chromium.org>
Reviewed-by: Aaron Gable <agable@chromium.org>
Commit-Queue: Albert J. Wong <ajwong@chromium.org>
Cr-Commit-Position: refs/heads/master@{#713133}

testing/buildbot/chromium.win.json

@@ -3086,7 +3086,7 @@
               "os": "Windows-10-15063"
             }
           ],
-          "shards": 12
+          "shards": 24
         }
       }
     ],

testing/buildbot/test_suite_exceptions.pyl

@@ -2084,6 +2084,9 @@
           '--target',
           'Release_x64',
         ],
+        'swarming': {
+          "shards": 24
+        },
       },
       'Win10 Tests x64 (dbg)': {
         'args': [