gh-419: Allow unstable builders to trigger on PRs (#420)

This intention of this PR is to make it possible to *manually trigger* also unstable buildbots on PRs using the `!buildbot` command (and labels).

The lists of "PR builders" are used in several places where I kept it to *only* stable PRs, because those other places didn't seem related to the manual triggering of buildbots on PRs.

Author: itamaro

master/master.cfg

@@ -299,12 +299,10 @@ for branch_num, (git_url, branchname, git_branch) in enumerate(git_branches):
 
 # Set up Pull Request builders
 
-pull_request_builders = []
+stable_pull_request_builders = []
+unstable_pull_request_builders = []
 
 for name, worker_name, buildfactory, stability, tier in BUILDERS:
-    if stability != STABLE:
-        continue
-
     if "Windows XP" in name or "VS9.0" in name:
         continue
     # bpo-39911: Python 3.9 dropped Windows 7 support
@@ -313,10 +311,14 @@ for name, worker_name, buildfactory, stability, tier in BUILDERS:
 
     buildername = name + " " + "PR"
 
+    if stability != STABLE:
+        unstable_pull_request_builders.append(buildername)
+        continue
+
     if any(pattern in buildername for pattern in NO_NOTIFICATION):
         continue
 
-    pull_request_builders.append(buildername)
+    stable_pull_request_builders.append(buildername)
 
     source = GitHub(repourl=git_url, **GIT_KWDS)
 
@@ -350,7 +352,7 @@ c["schedulers"].append(
         name="pull-request-scheduler",
         change_filter=util.ChangeFilter(filter_fn=should_pr_be_tested),
         treeStableTimer=30,  # seconds
-        builderNames=pull_request_builders,
+        builderNames=stable_pull_request_builders,
     )
 )
 
@@ -394,7 +396,7 @@ c["www"] = dict(
         "github": {
             "class": partial(
                 CustomGitHubEventHandler,
-                builder_names=pull_request_builders
+                builder_names=stable_pull_request_builders + unstable_pull_request_builders,
             ),
             "secret": str(settings.github_change_hook_secret),
             "strict": True,
@@ -458,7 +460,7 @@ c["services"].append(
     reporters.GitHubStatusPush(
         str(settings.github_status_token),
         generators=[
-            BuildStartEndStatusGenerator(builders=github_status_builders + pull_request_builders),
+            BuildStartEndStatusGenerator(builders=github_status_builders + stable_pull_request_builders),
         ],
         verbose=bool(settings.verbosity),
     )