Update mkdocs-material to 9.5.21.

This is an important update as it fixes the currently failing master
build.

ref: squidfunk/mkdocs-material#6983

.github/workflows/docker.yml

@@ -5,6 +5,6 @@ jobs:
   build:
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@b4ffde65f46336ab88eb53be808477a3936bae11 # v4.1.1
+    - uses: actions/checkout@44c2b7a8a4ea60a981eaca3cf939b5f4305c123b # v4.1.5
     - name: Build the Docker image
       run: docker build -t decred/dcrdevdocs:$(date +%s) .

.github/workflows/python.yml

@@ -9,9 +9,9 @@ jobs:
         python-version: [3.11]
 
     steps:
-    - uses: actions/checkout@b4ffde65f46336ab88eb53be808477a3936bae11 # v4.1.1
+    - uses: actions/checkout@44c2b7a8a4ea60a981eaca3cf939b5f4305c123b # v4.1.5
     - name: Set up Python ${{ matrix.python-version }}
-      uses: actions/setup-python@0a5c61591373683505ea898e09a3ea4f39ef2b9c # v5.0.0
+      uses: actions/setup-python@82c7e631bb3cdc910f68e0081d67478d79c6982d # v5.1.0
       with:
         python-version: ${{ matrix.python-version }}
     - name: Install dependencies

requirements.txt

@@ -1,2 +1,2 @@
-mkdocs-material==9.5.3
+mkdocs-material==9.5.21
 mkdocs-markdownextradata-plugin==0.2.5