weblayer: update version used for skew testing of 86

This is the most recent version we have for 86, and all tests
should pass with it.

BUG=1131958
TEST=test only change

Change-Id: I07abdd32a2ab86bbcb54e34c1737c17fd1f62745
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2454381Reviewed-by: Rakib Hasan <rmhasan@google.com>
Commit-Queue: Scott Violet <sky@chromium.org>
Cr-Commit-Position: refs/heads/master@{#814438}

testing/buildbot/chromium.android.fyi.json

@@ -606,7 +606,7 @@
             {
               "cipd_package": "chromium/testing/weblayer-x86",
               "location": "weblayer_instrumentation_test_M86",
-              "revision": "version:86.0.4240.16"
+              "revision": "version:86.0.4240.75"
             },
             {
               "cipd_package": "infra/tools/luci/logdog/butler/${platform}",

testing/buildbot/variants.pyl

@@ -325,7 +325,7 @@
         {
           'cipd_package': 'chromium/testing/weblayer-x86',
           'location': 'weblayer_instrumentation_test_M86',
-          'revision': 'version:86.0.4240.16',
+          'revision': 'version:86.0.4240.75',
         }
       ],
     },