Build: Bump mkdocs-section-index from 0.3.7 to 0.3.8 (#5)

Bumps [mkdocs-section-index](https://github.com/oprypin/mkdocs-section-index) from 0.3.7 to 0.3.8.
- [Release notes](https://github.com/oprypin/mkdocs-section-index/releases)
- [Commits](oprypin/mkdocs-section-index@v0.3.7...v0.3.8)

---
updated-dependencies:
- dependency-name: mkdocs-section-index
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

mkdocs/requirements.txt

@@ -25,4 +25,4 @@ mkdocs-autorefs==0.5.0
 mkdocs-gen-files==0.5.0
 mkdocs-material==9.4.1
 mkdocs-material-extensions==1.2
-mkdocs-section-index==0.3.7
+mkdocs-section-index==0.3.8