ci(dependabot): tolerate transient auto-merge conflicts

.github/workflows/dependabot-auto-merge.yml

@@ -64,11 +64,17 @@ jobs:
               status === "SKIPPED" ||
               status === "NEUTRAL";
 
-            const { data: pr } = await github.rest.pulls.get({
-              owner,
-              repo,
-              pull_number,
-            });
+            const wait = (ms) => new Promise((resolve) => setTimeout(resolve, ms));
+            const getPullRequest = async () => {
+              const { data } = await github.rest.pulls.get({
+                owner,
+                repo,
+                pull_number,
+              });
+              return data;
+            };
+
+            let pr = await getPullRequest();
 
             if (pr.user?.login !== "dependabot[bot]") {
               core.info(`PR #${pull_number} is no longer a Dependabot PR.`);
@@ -80,8 +86,14 @@ jobs:
               return;
             }
 
-            if (pr.mergeable === false) {
-              core.info(`PR #${pull_number} has merge conflicts.`);
+            for (let attempt = 1; attempt <= 6 && pr.mergeable === null; attempt += 1) {
+              core.info(`PR #${pull_number} mergeability is still being computed; retry ${attempt}/6.`);
+              await wait(5000);
+              pr = await getPullRequest();
+            }
+
+            if (pr.mergeable !== true) {
+              core.info(`PR #${pull_number} is not currently mergeable; skipping auto-merge.`);
               return;
             }
 
@@ -109,12 +121,21 @@ jobs:
               return;
             }
 
-            await github.rest.pulls.merge({
-              owner,
-              repo,
-              pull_number,
-              merge_method: "merge",
-            });
+            try {
+              await github.rest.pulls.merge({
+                owner,
+                repo,
+                pull_number,
+                merge_method: "merge",
+              });
+            } catch (error) {
+              if (error.status === 405 || error.status === 409) {
+                core.info(`PR #${pull_number} could not be merged right now: ${error.message}`);
+                return;
+              }
+
+              throw error;
+            }
 
             await github.rest.git.deleteRef({
               owner,