Bug 1673058 - Disable raptor-webext pageload tests on linux. r=perftest-reviewers,Bebe

This patch disable raptor-webext tests on linux.

Differential Revision: https://phabricator.services.mozilla.com/D94630

taskcluster/ci/test/raptor.yml

@@ -26,11 +26,13 @@ job-defaults:
                             warm:
                                 by-test-platform:
                                     (linux|windows|macos)(?!.*shippable).*: []
+                                    linux.*shippable.*: []
                                     default: ["mozilla-central"]
                             cold:
                                 by-test-platform:
                                     macosx.*64(?:-qr)?/opt: ["mozilla-central"]
                                     (linux|windows|macos)(?!.*shippable).*: []
+                                    linux.*shippable.*: []
                                     default: ["trunk", "mozilla-beta"]
                     default:
                         by-test-platform: