chore: simplify cicd rls script (#12413)

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## **Description**
Update the create release script to always assume the release branch has
been created already

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also include relevant motivation and context. Have in mind the following
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## **Related issues**

Fixes: 

https://github.com/MetaMask/metamask-mobile/actions/runs/11864495205/job/33068035826

## **Manual testing steps**

N/A

## **Screenshots/Recordings**

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### **Before**

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N/A - CI/CD Only

### **After**

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N/A - CI/CD Only

## **Pre-merge author checklist**

- [x] I’ve followed [MetaMask Contributor
Docs](https://github.com/MetaMask/contributor-docs) and [MetaMask Mobile
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Standards](https://github.com/MetaMask/metamask-mobile/blob/main/.github/guidelines/CODING_GUIDELINES.md).
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Not required for external contributors.

## **Pre-merge reviewer checklist**

- [x] I've manually tested the PR (e.g. pull and build branch, run the
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scripts/create-release-pr.sh

@@ -42,14 +42,9 @@ git config user.email metamaskbot@users.noreply.github.com
 echo "Fetching from remote..."
 git fetch
 
-# Check if the release branch already exists on the remote
-if git branch -a | grep -q "remotes/origin/${RELEASE_BRANCH_NAME}"; then
-    echo "Release branch exists on remote, checking out."
-    git checkout "${RELEASE_BRANCH_NAME}"
-else
-    echo "Release branch does not exist on remote, creating from ${BASE_BRANCH}."
-    git checkout -b "${RELEASE_BRANCH_NAME}"
-fi
+# Check out the existing release branch from the remote
+echo "Checking out the release branch: ${RELEASE_BRANCH_NAME}"
+git checkout "${RELEASE_BRANCH_NAME}"
 
 echo "Release Branch Checked Out"