[CI] Disable collapsing requests on premerge builders (llvm#565)

We have enough capacity on the premerge builders to not collapse
requests (test multiple commits at the same time). This ensures blame
lists are always limited to a single user.

Author: boomanaiden154

buildbot/osuosl/master/config/builders.py

@@ -3555,6 +3555,7 @@
             "premerge-us-west-linux-b2",
             "premerge-us-west-linux-b3",
         ],
+        "collapseRequests": False,
         "builddir": "premerge-monolithic-linux",
         "factory": AnnotatedBuilder.getAnnotatedBuildFactory(
             script="premerge/dispatch_job.py",
@@ -3579,6 +3580,7 @@
     },
     {
         "name": "premerge-monolithic-windows",
+        "collapseRequests": False,
         "workernames": [
             "premerge-us-central-windows-b1",
             "premerge-us-central-windows-b2",