Remove workaround for lean-update action (#196)

Author: TwoFX

.github/workflows/update.yml

@@ -18,11 +18,10 @@ jobs:
         uses: actions/checkout@v4
       - name: Get latest Lean nightly
         run: curl -s release.lean-lang.org | jq -r '.nightly[0].name' | sed 's/^/leanprover\/lean4:/' > lean-toolchain
-      - name: Append empty lines to lake-manifest.json to trick lean-update into leaving the lean-toolchain file alone
-        run: printf '\n%.0s' {1..10} >> lake-manifest.json
       - name: Update Lean project
         uses: leanprover-community/lean-update@main
         with:
           update_if_modified: lean-toolchain
           on_update_succeeds: "commit"
-          on_update_fails: "issue"
+          on_update_fails: "issue"
+          update_lean_toolchain: "never"