fix(git-node): prepare_release resilient checkout

In `git node release --prepare` when checking out a new proposal branch
make sure it's also possible to update an already existing branch of
that same name instead of failing and terminating the automation.

Author: ruyadorno

Diff for: lib/prepare_release.js

@@ -93,9 +93,9 @@ export default class ReleasePreparation extends Session {
     } = this;
 
     // Create new proposal branch.
-    cli.startSpinner(`Creating new proposal branch for ${newVersion}`);
+    cli.startSpinner(`Switching to proposal branch for ${newVersion}`);
     const proposalBranch = await this.createProposalBranch(releaseBranch);
-    cli.stopSpinner(`Created new proposal branch for ${newVersion}`);
+    cli.stopSpinner(`Switched to proposal branch for ${newVersion}`);
 
     const success = await this.cherryPickSecurityPRs(filterLabels);
     if (!success) {
@@ -201,9 +201,9 @@ export default class ReleasePreparation extends Session {
     }
 
     // Create new proposal branch.
-    cli.startSpinner(`Creating new proposal branch for ${newVersion}`);
+    cli.startSpinner(`Switching to proposal branch for ${newVersion}`);
     await this.createProposalBranch();
-    cli.stopSpinner(`Created new proposal branch for ${newVersion}`);
+    cli.stopSpinner(`Switched to proposal branch for ${newVersion}`);
 
     if (this.isLTSTransition) {
       // For releases transitioning into LTS, fetch the new code name.
@@ -535,7 +535,7 @@ export default class ReleasePreparation extends Session {
 
     await runAsync('git', [
       'checkout',
-      '-b',
+      '-B',
       proposalBranch,
       base
     ]);