Skip spring on app test

spring 4.3.0 on old version of Rails (e.g. 6.x) causes
`initialize': Rails::Application is abstract, you cannot instantiate it directly. (RuntimeError)

Author: amatsuda

test/test_app.sh

@@ -21,7 +21,7 @@ set -o pipefail
 
 export MAKEFLAGS=-j$(nproc)
 
-rails new todo --skip-bundle
+rails new todo --skip-bundle --skip-spring
 cd todo
 
 export PATH=$PWD/bin:$PATH