Bug 1642720 - Disable reftests on win7/mingw builds. r=tjr

These reftests seem to hang quite frequently, caused by the content process
hanging on file create/open operations. See dependencies of bug 1642719 for
some examples.

Differential Revision: https://phabricator.services.mozilla.com/D77875

taskcluster/ci/test/test-platforms.yml

@@ -326,7 +326,7 @@ windows10-64-mingwclang/opt:
 windows7-32-mingwclang/debug:
     build-platform: win32-mingwclang/debug
     test-sets:
-        - mingwclang-tests-debug
+        - mingwclang-win7-tests-debug
 
 windows7-32-mingwclang/opt:
     build-platform: win32-mingwclang/opt

taskcluster/ci/test/test-sets.yml

@@ -332,6 +332,24 @@ mingwclang-tests-debug:
     - reftest
     - telemetry-tests-client
 
+# The following is the same as the above block, minus reftests.
+# Reftests were disabled due to frequent hangs; see bug 1642719
+# for re-enabling.
+mingwclang-win7-tests-debug:
+    - cppunit
+    - firefox-ui-functional-local
+    - firefox-ui-functional-remote
+    - mochitest-a11y
+    - mochitest-chrome-gpu
+    - mochitest-plain-gpu
+    - mochitest-webgl1-core
+    - mochitest-webgl1-ext
+    - mochitest-webgl2-core
+    - mochitest-webgl2-ext
+    - mochitest-webgpu
+    # - reftest - disabled, see bug 1642719
+    - telemetry-tests-client
+
 mingwclang-tests-opt:
     - cppunit
     - mochitest-chrome-gpu