Restore mergecommitsha implementation for RemoveMergedTestMerges

src/Tgstation.Server.Host.Utils.GitLab.GraphQL/GQL/Queries/GetMergeRequest.graphql

@@ -5,6 +5,7 @@ query GetMergeRequest($project: ID!, $number: String!) {
             description
             title
             diffHeadSha
+            mergeCommitSha
             webUrl
             iid
             id

src/Tgstation.Server.Host.Utils.GitLab.GraphQL/GQL/Queries/GetMergeRequests.graphql

@@ -4,6 +4,7 @@ query GetMergeRequests($project: ID!, $numbers: [String!]!) {
             nodes {
                 state
                 diffHeadSha
+                mergeCommitSha
                 closedAt
                 iid
                 id

src/Tgstation.Server.Host/Components/Deployment/Remote/GitLabRemoteDeploymentManager.cs

@@ -89,10 +89,10 @@ async ValueTask CheckRemoveMR(IGetMergeRequests_Project_MergeRequests_Nodes? mer
 				if (mergeRequest.State != MergeRequestState.Merged)
 					return;
 
-				var diffHeadSha = mergeRequest.DiffHeadSha;
-				if (diffHeadSha == null)
+				var mergeCommitSha = mergeRequest.MergeCommitSha;
+				if (mergeCommitSha == null)
 				{
-					Logger.LogWarning("MergeRequest #{id} had no DiffHeadSha!", mergeRequest.Iid);
+					Logger.LogWarning("MergeRequest #{id} had no MergeCommitSha!", mergeRequest.Iid);
 					return;
 				}
 
@@ -116,7 +116,7 @@ async ValueTask CheckRemoveMR(IGetMergeRequests_Project_MergeRequests_Nodes? mer
 				}
 
 				// We don't just assume, actually check the repo contains the merge commit.
-				if (await repository.CommittishIsParent(diffHeadSha, cancellationToken))
+				if (await repository.CommittishIsParent(mergeCommitSha, cancellationToken))
 					newList.Remove(
 						newList.First(
 							potential => potential.Number == number));