Dependabot creates PR for yanked python dependency

**Package ecosystem**
pip poetry

**Package manager version**
poetry 1.1.11

**Language version**
Python 3.6

**Manifest location and content prior to update**
https://github.com/h3llrais3r/Auto-Subliminal/blob/development/pyproject.toml

**dependabot.yml content**
```
# Please see the documentation for all configuration options:
# https://help.github.com/github/administering-a-repository/configuration-options-for-dependency-updates

version: 2
updates:

# Maintain dependencies for GitHub Actions
- package-ecosystem: github-actions
directory: "/"
target-branch: development
schedule:
interval: daily

# Maintain dependencies for pip (also includes poetry)
- package-ecosystem: pip
directory: "/"
schedule:
interval: daily
target-branch: development

# Maintain dependencies for npm
- package-ecosystem: npm
directory: "/web/autosubliminal"
target-branch: development
schedule:
interval: daily
```

**Updated dependency**
Bump gitpython from 3.1.18 to 3.1.20
https://github.com/h3llrais3r/Auto-Subliminal/pull/565

**What you expected to see, versus what you actually saw**
Dependabot not creating a PR for a yanked version.
https://pypi.org/pypi/GitPython/3.1.20/json (marked as yanked)

**Native package manager behavior**

**Images of the diff or a link to the PR, issue or logs**
```
proxy | 2021/11/15 18:55:06 [157] GET https://pypi.org:443/simple/pip/
proxy | 2021/11/15 18:55:06 [157] 200 https://pypi.org:443/simple/pip/
proxy | 2021/11/15 18:55:07 [159] GET https://pypi.org:443/pypi/gitpython/json
proxy | 2021/11/15 18:55:07 [159] 301 https://pypi.org:443/pypi/gitpython/json
proxy | 2021/11/15 18:55:07 [161] GET https://pypi.org:443/pypi/GitPython/json
proxy | 2021/11/15 18:55:07 [161] 200 https://pypi.org:443/pypi/GitPython/json
proxy | 2021/11/15 18:55:07 [163] GET https://pypi.org:443/pypi/gitpython/3.1.24/json
proxy | 2021/11/15 18:55:07 [163] 301 https://pypi.org:443/pypi/gitpython/3.1.24/json
proxy | 2021/11/15 18:55:07 [165] GET https://pypi.org:443/pypi/GitPython/3.1.24/json
proxy | 2021/11/15 18:55:07 [165] 200 https://pypi.org:443/pypi/GitPython/3.1.24/json
proxy | 2021/11/15 18:55:07 [167] GET https://pypi.org:443/pypi/gitpython/3.1.23/json
proxy | 2021/11/15 18:55:07 [167] 301 https://pypi.org:443/pypi/gitpython/3.1.23/json
proxy | 2021/11/15 18:55:07 [169] GET https://pypi.org:443/pypi/GitPython/3.1.23/json
proxy | 2021/11/15 18:55:07 [169] 200 https://pypi.org:443/pypi/GitPython/3.1.23/json
proxy | 2021/11/15 18:55:07 [171] GET https://pypi.org:443/pypi/gitpython/3.1.22/json
proxy | 2021/11/15 18:55:07 [171] 301 https://pypi.org:443/pypi/gitpython/3.1.22/json
proxy | 2021/11/15 18:55:07 [173] GET https://pypi.org:443/pypi/GitPython/3.1.22/json
proxy | 2021/11/15 18:55:07 [173] 200 https://pypi.org:443/pypi/GitPython/3.1.22/json
proxy | 2021/11/15 18:55:07 [175] GET https://pypi.org:443/pypi/gitpython/3.1.20/json
proxy | 2021/11/15 18:55:07 [175] 301 https://pypi.org:443/pypi/gitpython/3.1.20/json
proxy | 2021/11/15 18:55:08 [177] GET https://pypi.org:443/pypi/GitPython/3.1.20/json
proxy | 2021/11/15 18:55:08 [177] 200 https://pypi.org:443/pypi/GitPython/3.1.20/json
proxy | 2021/11/15 18:55:10 [179] GET https://pypi.org:443/pypi/autosubliminal/json/
proxy | 2021/11/15 18:55:10 [179] 404 https://pypi.org:443/pypi/autosubliminal/json/
updater | INFO Requirements to unlock own
proxy | 2021/11/15 18:55:11 [181] GET https://pypi.org:443/pypi/autosubliminal/json/
proxy | 2021/11/15 18:55:11 [181] 404 https://pypi.org:443/pypi/autosubliminal/json/
updater | INFO Requirements update strategy bump_versions
proxy | 2021/11/15 18:55:11 [183] GET https://pypi.org:443/pypi/autosubliminal/json/
proxy | 2021/11/15 18:55:11 [183] 404 https://pypi.org:443/pypi/autosubliminal/json/
proxy | 2021/11/15 18:55:11 [185] GET https://pypi.org:443/pypi/autosubliminal/json/
proxy | 2021/11/15 18:55:11 [185] 404 https://pypi.org:443/pypi/autosubliminal/json/
proxy | 2021/11/15 18:55:11 [187] GET https://pypi.org:443/pypi/autosubliminal/json/
proxy | 2021/11/15 18:55:11 [187] 404 https://pypi.org:443/pypi/autosubliminal/json/
proxy | 2021/11/15 18:55:11 [189] GET https://pypi.org:443/pypi/autosubliminal/json/
proxy | 2021/11/15 18:55:11 [189] 404 https://pypi.org:443/pypi/autosubliminal/json/
updater | INFO Updating gitpython from 3.1.18 to 3.1.20
```

Start with the pip/Poetry update path described in the issue, using pyproject.toml and the provided dependabot.yml configuration, and inspect the PyPI JSON response for GitPython 3.1.20. Reproduce the update against the linked dependency PR and verify that yanked releases are handled according to the expected behavior without blocking valid updates.

Written by the indexing model from the issue text.