Ruby version mismatch

### Is there an existing issue for this?

- [X] I have searched the existing issues

### Package ecosystem

Bundler

### Package manager version

2.5.6

### Language version

3.3.0

### Manifest location and content before the Dependabot update

/Gemfile

### dependabot.yml content

version: 2
updates:
- package-ecosystem: bundler
directory: /
registries: "*"
schedule:
interval: daily

### Updated dependency

_No response_

### What you expected to see, versus what you actually saw

I've added Dependabot to a Ruby 3.3.0 app. Dependabot couldn't resolve dependencies because `prometheus-client-mmap` depends on >= Ruby 2.7.0 but Dependabot was somehow using Ruby 2.6.9. The error message:

```
Handled error whilst updating : dependency_file_not_resolvable {:message=>"Could not find compatible versions\n\nBecause prometheus-client-mmap >= 1.1.0, < 1.1.1 depends on Ruby >= 2.7, < 3.4.dev\n and prometheus-client-mmap = 1.1.0 depends on Ruby >= 2.7.0,\n and current Ruby version is = 2.6.9,\n version solving has failed."}
```

My app declares the Ruby version as 3.3.0 via `.ruby-version`.

Looking for a public repo example, I've seen this for `dependabot-core`: https://github.com/dependabot/dependabot-core/actions/runs/9678038683/job/26700936769 It's the same type of error as mine.

### Native package manager behavior

_No response_

### Images of the diff or a link to the PR, issue, or logs

_No response_

### Smallest manifest that reproduces the issue

_No response_

Start by reviewing the /Gemfile, .ruby-version, and dependabot.yml configuration described in the report, then compare them with the dependency-resolution log showing Ruby 2.6.9. Check the referenced dependabot-core workflow for a related reproduction. Done means the Bundler update process resolves dependencies against the application's declared Ruby 3.3.0 version.

Written by the indexing model from the issue text.