Fix release script crash when no releases exist for new major version (#5487)

When creating a release for a new major version (e.g., v5), the script
crashes with TypeError because no previous releases with that prefix
exist. This adds fallback logic to use the previous major version
(e.g., v4) for comparison instead.

Co-authored-by: azure-pipelines-bot <azure-pipelines-bot@microsoft.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: 3 people

release/createReleaseBranch.js

@@ -139,10 +139,24 @@ async function fetchPRsSincePreviousReleaseAndEditReleaseNotes(newRelease, callb
 
         var filteredReleases = latestReleases.data.filter(release => !release.draft); // consider only pre-releases and published releases
 
-        var releaseTagPrefix = 'v' + newRelease.split('.')[0];
+        var majorVersion = parseInt(newRelease.split('.')[0]);
+        var releaseTagPrefix = 'v' + majorVersion;
         console.log(`Getting latest release starting with ${releaseTagPrefix}`);
 
         var latestReleaseInfo = filteredReleases.find(release => release.tag_name.toLowerCase().startsWith(releaseTagPrefix.toLowerCase()));
+
+        // Fall back to previous major version if no releases found for current major version
+        if (!latestReleaseInfo && majorVersion > 0) {
+            var fallbackPrefix = 'v' + (majorVersion - 1);
+            console.log(`No releases found with prefix ${releaseTagPrefix}, falling back to ${fallbackPrefix}`);
+            latestReleaseInfo = filteredReleases.find(release => release.tag_name.toLowerCase().startsWith(fallbackPrefix.toLowerCase()));
+        }
+
+        if (!latestReleaseInfo) {
+            console.log(`Error: No releases found with prefix ${releaseTagPrefix} or fallback. Aborting.`);
+            process.exit(-1);
+        }
+
         console.log(`Previous release tag with ${latestReleaseInfo.tag_name} and published date is: ${latestReleaseInfo.published_at}`)
 
         try {