chore(deps): bump squidfunk/mkdocs-material in /docs

Bumps squidfunk/mkdocs-material from `868ad4d` to `51b8714`.

---
updated-dependencies:
- dependency-name: squidfunk/mkdocs-material
  dependency-version: 51b87149d227691486b5f08993d28c65ca7e4990010664b697265b8e6fcd5287
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

docs/Dockerfile

@@ -1,5 +1,5 @@
 # v9.1.18
-FROM squidfunk/mkdocs-material@sha256:868ad4d39fb5865b72d00173ade00f4eae2b38dde7ff790a011cc44ce4a8ff8e
+FROM squidfunk/mkdocs-material@sha256:51b87149d227691486b5f08993d28c65ca7e4990010664b697265b8e6fcd5287
 # pip-compile --generate-hashes --output-file=requirements.txt requirements.in
 COPY requirements.txt /tmp/
 RUN pip install --require-hashes -r /tmp/requirements.txt