Do not explicitly install Python

Rely on the version(s) provided by the runner images.

.github/workflows/build-data-archive.yml

@@ -28,11 +28,6 @@ jobs:
           wget -q -O - 'https://github.com/casey/just/releases/download/1.38.0/just-1.38.0-x86_64-unknown-linux-musl.tar.gz' | tar xvz just --to-stdout > /usr/local/bin/just
           chmod u+x /usr/local/bin/just
 
-      - name: Set up Python
-        uses: actions/setup-python@v5
-        with:
-          python-version: "3.12"
-
       - name: Fetch contributors
         run: just fetch-contributors
 

.github/workflows/validate.yml

@@ -41,10 +41,5 @@ jobs:
       - name: Validate party TOML files
         run: just validate-parties
 
-      - name: Set up Python
-        uses: actions/setup-python@v5
-        with:
-          python-version: "3.12"
-
       - name: Ensure that parties are in the past
         run: just validate-party-dates