Bug 1588631 [wpt PR 19682] - Reduce number of chunks for master runs, a=testonly

Automatic update from web-platform-tests
Reduce number of reftest chunks for master runs

Reduce number of reftest chunks to 5 to save some resources; these
never limit overall e2e time.

--

wpt-commits: a536bc234b54a8062e4cfa01c05becbc49cdea52
wpt-pr: 19682

testing/web-platform/tests/.taskcluster.yml

@@ -40,16 +40,11 @@ tasks:
               - [testharness, 13, 15]
               - [testharness, 14, 15]
               - [testharness, 15, 15]
-              - [reftest, 1, 10]
-              - [reftest, 2, 10]
-              - [reftest, 3, 10]
-              - [reftest, 4, 10]
-              - [reftest, 5, 10]
-              - [reftest, 6, 10]
-              - [reftest, 7, 10]
-              - [reftest, 8, 10]
-              - [reftest, 9, 10]
-              - [reftest, 10, 10]
+              - [reftest, 1, 5]
+              - [reftest, 2, 5]
+              - [reftest, 3, 5]
+              - [reftest, 4, 5]
+              - [reftest, 5, 5]
               - [wdspec, 1, 1]
             each(chunk):
               taskId: {$eval: 'as_slugid(browser.name + browser.channel + chunk[0] + str(chunk[1]))'}