CI: Use action to install leiningen

We use the same action in other projects

(cherry picked from commit fa7ff2a)

Author: bastelfreak

.github/workflows/pr.yml

@@ -32,6 +32,9 @@ jobs:
       - name: Install Clojure tools
         uses: DeLaGuardo/[email protected]
         with:
+          # Install just one or all simultaneously
+          # The value must indicate a particular version of the tool, or use 'latest'
+          # to always provision the latest version
           lein: latest # Leiningen
       - run: lein test