test: shellcheck fix

Author: lrm25

tests/test_rest_checksum.sh

@@ -27,7 +27,6 @@ test_file="test_file"
   if [ "$DIRECT" != "true" ]; then
     skip "https://github.com/versity/versitygw/issues/1104"
   fi
-  test_file="test_file"
   run setup_bucket_and_file "$BUCKET_ONE_NAME" "$test_file"
   assert_success