fix: use lake test if test.sh is missing from lean4checker (#160)

test.sh was removed in lean4check 4.27.0

note, Lean version >= 4.28.x will use the built in leanchecker so this
only affects 4.27.0

Co-authored-by: Austin Letson <austin.letson@axiomatic-ai.com>

Author: austinletson

scripts/run_leanchecker.sh

@@ -32,7 +32,11 @@ git checkout "$toolchain_version"
 cp ../lean-toolchain .
 
 lake build
-./test.sh
+if [ -f ./test.sh ]; then
+  ./test.sh
+else
+  lake test
+fi
 )
 
 echo "Running external lean4checker"