New attempt to streamline downstream merges.

Author: gfraiteur

src/PostSharp.Engineering.BuildTools/ContinuousIntegration/GitHubHelper.cs

@@ -6,10 +6,13 @@
 using Octokit.GraphQL.Model;
 using PostSharp.Engineering.BuildTools.Build;
 using PostSharp.Engineering.BuildTools.Utilities;
+using System;
 using System.Collections.Generic;
+using System.Diagnostics;
 using System.Diagnostics.CodeAnalysis;
 using System.Linq;
 using System.Text;
+using System.Threading;
 using System.Threading.Tasks;
 using Connection = Octokit.GraphQL.Connection;
 using Environment = System.Environment;
@@ -181,7 +184,17 @@ bool TryConnectRestApis( [NotNullWhen( true )] out GitHubClient? creatorClient,
 
             return default;
         }
-        
+
+        // Wait until the mergeability is known.
+        var waitStatusStopwatch = Stopwatch.StartNew();
+
+        while ( pullRequest.Mergeable == null && waitStatusStopwatch.Elapsed < TimeSpan.FromMinutes( 1 ) )
+        {
+            console.WriteMessage( $"Waiting until we know whether the PR is mergeable (waited {waitStatusStopwatch.Elapsed} so far)." );
+            Thread.Sleep( 200 );
+            pullRequest = await creatorGitHub.PullRequest.Get( repository.Owner, repository.Name, pullRequest.Number );
+        }
+
         // Check status checks (if any required)
         if ( pullRequest.Mergeable == true )
         {