Fix the v3 backport message to use v3-backport-PR (#9777)

* Fix the v3 backport message to use v3-backport-PR

* fixup! actually create the v3 PR

* fixup! this will not happen again!

Author: vicb

.github/workflows/open-v3-maintenance-prs.yml

@@ -63,4 +63,4 @@ jobs:
         with:
           header: v3-backport
           message: |
-            These changes have been automatically backported to Wrangler v3 :tada: You can view the automatically updated PR at https://github.com/cloudflare/workers-sdk/compare/v3-maintenance...v3-maintenance-${{ github.event.number }}. Please check that PR for correctness, and make sure it's merged after this one. Thank you for helping us keep Wrangler v3 supported!
+            These changes have been automatically backported to Wrangler v3 :tada: You can view the automatically updated PR at https://github.com/cloudflare/workers-sdk/compare/v3-maintenance...v3-backport-${{ github.event.number }}. Please check that PR for correctness, and make sure it's merged after this one. Thank you for helping us keep Wrangler v3 supported!

tools/deployments/open-v3-pr.ts

@@ -6,11 +6,10 @@ import parseChangeset from "@changesets/parse";
 if (require.main === module) {
 	if (isWranglerPatch(process.env.FILES as string)) {
 		// Create a new branch for the v3 maintenance PR
-		execSync(`git checkout -b v3-backport-${process.env.PR_NUMBER} -f`);
+		const branch = `v3-backport-${process.env.PR_NUMBER}`;
+		execSync(`git checkout -b ${branch} -f`);
 
-		execSync(
-			`git rebase --onto origin/v3-maintenance origin/main v3-backport-${process.env.PR_NUMBER}`
-		);
+		execSync(`git rebase --onto origin/v3-maintenance origin/main ${branch}`);
 
 		execSync(`git push origin HEAD --force`);
 
@@ -23,7 +22,7 @@ if (require.main === module) {
 					`create`,
 					`--base`,
 					`v3-maintenance`,
-					`--head v3-maintenance-${process.env.PR_NUMBER}`,
+					`--head ${branch}`,
 					`--label "skip-pr-description-validation"`,
 					`--label "skip-v3-pr"`,
 					`--label "v3-backport"`,