Bug 1621601 - Disable socket process sandbox for xpcshell tests r=haik

Differential Revision: https://phabricator.services.mozilla.com/D66790

--HG--
extra : moz-landing-system : lando

testing/xpcshell/runxpcshelltests.py

@@ -1025,6 +1025,8 @@ class XPCShellTests(object):
         # compatible with the sandbox.
         self.env["MOZ_DISABLE_CONTENT_SANDBOX"] = "1"
 
+        self.env["MOZ_DISABLE_SOCKET_PROCESS_SANDBOX"] = "1"
+
         if self.enable_webrender:
             self.env["MOZ_WEBRENDER"] = "1"
             self.env["MOZ_ACCELERATED"] = "1"