Impact analysis of fixed events - Discrepancy between specification and implementation

**Describe the bug**

The OSV.dev implementation of impact analysis diverges from the [specification](https://ossf.github.io/osv-schema/#evaluation) for `fixed` events. They seem to be treated like `limit` events, differently from the [example](https://ossf.github.io/osv-schema/#limit-events) in the specification.

**To Reproduce**

1. clone https://github.com/RomainLefeuvre/osv.dev
2. setup your python virtualenv as described in the osv documentation
3. from the root level of the repo, execute `python -m osv.analyze_tool --format json "./osv/osv_bug/vuln.json"`
4. it prints the vulnerable commits:
```
❯ python -m osv.analyze_tool --format json "./osv/osv_bug/vuln.json"
INFO:root:Analyzing ./osv/osv_bug/vuln.json
INFO:root:Cloning https://github.com/RomainLefeuvre/osv_issue_minimal_example.git to /tmp/tmpakfa5gj5
INFO:root:Finding equivalent regress commit to d241812d2722d573a7b096d44d139946d8dcb484 in refs/remotes/origin/main in https://github.com/RomainLefeuvre/osv_issue_minimal_example.git
INFO:root:Finding equivalent fix commit to 80f15009d903ac95ffc5a5a07a3a213e4980bb62 in refs/remotes/origin/main in https://github.com/RomainLefeuvre/osv_issue_minimal_example.git
INFO:root:Getting commits d241812d2722d573a7b096d44d139946d8dcb484..80f15009d903ac95ffc5a5a07a3a213e4980bb62 from https://github.com/RomainLefeuvre/osv_issue_minimal_example.git
AnalyzeResult(has_changes=False, commits={'868d891cffe96cd67b2abac82c62ade7219af9b5', 'd241812d2722d573a7b096d44d139946d8dcb484', 'e54222cfdedd86a37dc37d999ebc63dccf3fc9da', 'ec5e313170f68d3fc575d107a8b92d43ae140249'})
INFO:root:No changes required.
```
I.e.:
- `868d891cffe96cd67b2abac82c62ade7219af9b5` (C)
- `d241812d2722d573a7b096d44d139946d8dcb484` (X)
- `e54222cfdedd86a37dc37d999ebc63dccf3fc9da` (A)
- `ec5e313170f68d3fc575d107a8b92d43ae140249` (B)

Note that :
- The history of the repo at matches the example in the specification:

- The [toy vulnerability](https://github.com/RomainLefeuvre/osv.dev/blob/6b03f4d9723c5d14249c24b67bf032a9ce271633/osv/osv_bug/vuln.json?plain=1#L1-L30) matches also the one used in the example :

```
{
"id": "test",
"details": "test",
"modified": "2024-01-10T08:29:31.368677Z",
"published": "2024-01-10T08:29:31.368677Z",
"affected": [
{
"package": {
"name": "test",
"ecosystem": "PyPI",
"purl": "test"
},
"ranges": [
{
"type": "GIT",
"repo": "https://github.com/RomainLefeuvre/osv_issue_minimal_example.git",
"events": [
{
"introduced": "d241812d2722d573a7b096d44d139946d8dcb484"
},
{
"fixed": "80f15009d903ac95ffc5a5a07a3a213e4980bb62"
}
]
}
],
"schema_version": "1.6.0"
}
]
}
```

**Expected behaviour**
D, F and E should also be reported as vulnerable as described:

> Without an explicit limit, the list of computed affected commits will be X, A, B, C, D, E, F. This is the desired behaviour in most cases.