Deployment policy 404 when protected branches is enabled

## Problem Description

Using the latest environment.js code in the repo.
In settings.yml when wanting to create an environment when the same name environment is already there. We get a 404 during PR mode which crashes the app. Possibly also happens on main.

### What is actually happening

What happens is that the existing environment has `protected_branches: true` which is mutually exclusive with deployment-branch-policies.
In PR mode a 404 then happens because it wrongly requests to list the custom branch policies. This results in a crash of the app.

The environment we want to update has custom deployment branch policies setup:
```
environments:
- name: release
deployment_branch_policy:
protected_branches: false
custom_branch_policies:
- "main"
- "release/*"
- "hotfix/*.*.*"
```

### What is the expected behavior
When you get the environment you see if it has protected_branches set to true. If false, only then do you try to retrieve custom_branch_policies.

### Error output, if available

```
{"level":20,"time":1737568096854,"pid":25,"hostname":"safe-settings-cf64dd6bd-4dsrv","name":"probot","name":"probot","name":"octokit","msg":"GitHub request: GET https://api.github.com/repos/x/x/environments/release/deployment-branch-policies - 404"}
/opt/safe-settings/node_modules/probot/node_modules/@octokit/request/dist-node/index.js:86
const error = new requestError.RequestError(toErrorMessage(data), status, {
^

RequestError [HttpError]: Not Found
at /opt/safe-settings/node_modules/probot/node_modules/@octokit/request/dist-node/index.js:86:21
at process.processTicksAndRejections (node:internal/process/task_queues:95:5)
at async sendRequestWithRetries (/opt/safe-settings/node_modules/octokit-auth-probot/node_modules/@octokit/auth-app/dist-node/index.js:398:12)
at async Job.doExecute (/opt/safe-settings/node_modules/bottleneck/light.js:405:18) {
status: 404,
response: {
url: 'https://api.github.com/repos/x/x/environments/release/deployment-branch-policies',
status: 404,
headers: {
'access-control-allow-origin': '*',
'access-control-expose-headers': 'ETag, Link, Location, Retry-After, X-GitHub-OTP, X-RateLimit-Limit, X-RateLimit-Remaining, X-RateLimit-Used, X-RateLimit-Resource, X-RateLimit-Reset, X-OAuth-Scopes, X-Accepted-OAuth-Scopes, X-Poll-Interval, X-GitHub-Media-Type, X-GitHub-SSO, X-GitHub-Request-Id, Deprecation, Sunset',
'content-encoding': 'gzip',
'content-security-policy': "default-src 'none'",
'content-type': 'application/json; charset=utf-8',
date: 'Wed, 22 Jan 2025 17:48:16 GMT',
'referrer-policy': 'origin-when-cross-origin, strict-origin-when-cross-origin',
server: 'github.com',
'strict-transport-security': 'max-age=31536000; includeSubdomains; preload',
'transfer-encoding': 'chunked',
vary: 'Accept-Encoding, Accept, X-Requested-With',
'x-accepted-github-permissions': 'actions=read',
'x-content-type-options': 'nosniff',
'x-frame-options': 'deny',
'x-github-api-version-selected': '2022-11-28',
'x-github-media-type': 'github.v3; format=json',
'x-github-request-id': '0C43:11797C:DBF949:E1D473:67912F60',
'x-ratelimit-limit': '15000',
'x-ratelimit-remaining': '14457',
'x-ratelimit-reset': '1737569696',
'x-ratelimit-resource': 'core',
'x-ratelimit-used': '543',
'x-xss-protection': '0'
},
data: {
message: 'Not Found',
documentation_url: 'https://docs.github.com/rest/deployments/branch-policies#list-deployment-branch-policies',
status: '404'
}
},
request: {
method: 'GET',
url: 'https://api.github.com/repos/x/environments/release/deployment-branch-policies',
headers: {
accept: 'application/vnd.github.v3+json',
'user-agent': 'probot/12.3.4 octokit-core.js/3.6.0 Node.js/20.18.1 (linux; x64)',
authorization: 'token [REDACTED]'
},
request: { hook: [Function: bound bound register] }
}
}
```

## Context

### Are you using the hosted instance of probot/settings or running your own?

### If running your own instance, are you using it with github.com or GitHub Enterprise?

#### Version of probot/settings

#### Version of GitHub Enterprise