update github action to also test on new lean version 4.14.0

Author: awalterschulze

.github/workflows/check_proofs.yml

@@ -22,7 +22,7 @@ jobs:
         run: |
           curl -O --location https://raw.githubusercontent.com/leanprover/elan/master/elan-init.sh
           chmod u+x elan-init.sh
-          ./elan-init.sh -y --default-toolchain leanprover/lean4:v4.11.0-rc2
+          ./elan-init.sh -y --default-toolchain leanprover/lean4:v4.14.0
           echo "Adding location $HOME/.elan/bin to PATH..."
           echo "$HOME/.elan/bin" >> $GITHUB_PATH