fix: massage/truncate variable length comments (#7819)

Closes #7775

lib/workers/branch/index.ts

@@ -619,6 +619,7 @@ export async function processBranch(
           content += `##### File name: ${error.lockFile}\n\n`;
           content += `\`\`\`\n${error.stderr}\n\`\`\`\n\n`;
         });
+        content = platform.getPrBody(content);
         if (
           !(
             config.suppressNotifications.includes('artifactErrors') ||

lib/workers/pr/index.ts

@@ -425,6 +425,7 @@ export async function ensurePr(
       if (config.branchAutomergeFailureMessage === 'branch status error') {
         content += '\n___\n * Branch has one or more failed status checks';
       }
+      content = platform.getPrBody(content);
       logger.debug('Adding branch automerge failure message to PR');
       // istanbul ignore if
       if (config.dryRun) {