chore: add git checkout to workflows (#33539)

### Issue # (if applicable)

n/a

### Reason for this change

fix workflows failing with 
`error: failed to push some refs to 'https://github.com/aws/aws-cdk'`

### Description of changes

add `git checkout` to exit detached HEAD state before committing/pushing

### Describe any new or updated permissions being added

n/a

### Description of how you validated changes

Validated previously and confirmed workflow succeeded

### Checklist
- [x] My code adheres to the [CONTRIBUTING GUIDE](https://github.com/aws/aws-cdk/blob/main/CONTRIBUTING.md) and [DESIGN GUIDELINES](https://github.com/aws/aws-cdk/blob/main/docs/DESIGN_GUIDELINES.md)

----

*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

Author: gracelu0

.github/workflows/analytics-metadata-updater.yml

@@ -55,6 +55,7 @@ jobs:
             exit 1
           fi
 
+          git checkout -B ${{ github.event.pull_request.head.ref }}
           git add .
           git commit -m "chore: update analytics metadata blueprints"
           git push origin ${{ github.event.pull_request.head.ref }}

.github/workflows/lambda-runtime-tests.yml

@@ -52,6 +52,7 @@ jobs:
             exit 1
           fi
 
+          git checkout -B ${{ github.event.pull_request.head.ref }}
           git add .
           git commit -m "chore: update lambda runtime integration tests"
           git push origin ${{ github.event.pull_request.head.ref }}