Can't add email notifications for a branch with a / in the name

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- [X] I have checked to see if my question is addressed in the [FAQ](https://github.com/aws-amplify/amplify-hosting/blob/master/FAQ.md).
- [X] I have [searched for duplicate or closed issues](https://github.com/aws-amplify/amplify-hosting/issues?q=is%3Aissue+).
- [X] I have read the guide for [submitting bug reports](https://github.com/aws-amplify/amplify-hosting/blob/master/CONTRIBUTING.md).
- [X] I have done my best to include a minimal, self-contained set of instructions for consistently reproducing the issue.
- [X] I have removed any sensitive information from my code snippets and submission.

### App Id

dbgrrzo2f6e8h

### AWS Region

us-east-1

### Amplify Hosting feature

Notifications

### Describe the bug

I'm trying to add an email notification for a branch called `release/production`. When I select `release/production` from the Branch dropdown, the Save button on the page turns grey and can't be clicked. Other branches seem to work fine, though.

### Expected behavior

I should be able to click the Save button after selecting the `release/production` branch.

### Reproduction steps

1. Make a branch called `release/production`.
2. Attempt to make an email notification for that branch.

### Works for `master`

### Doesn't work for `release/production`

### Build Settings

_No response_

### Log output

```
# Put your logs below this line

```

### Additional information

_No response_

Start by reproducing the issue in Amplify Hosting Notifications with a branch named `release/production`, comparing it with `master` in the branch dropdown. Trace why selecting the slash-containing branch disables Save; done when an email notification can be saved for that branch without breaking other branches.

Written by the indexing model from the issue text.