Make Suspenders fail if running with an unsupported Rails version

[thiagoa]

The suspenders command does not fail when accidentally picking up an unsupported Rails version, which may lead to very strange errors. I had a problem with it picking up Rails 6.1 (actually, Rails 6.1 was uninstalled but it picked up railties 6.1.4.1, which was still installed), so to fix it I installed Rails 6.0 and ran suspenders with the following command:

suspenders _6.0.4.1_ my-app

[stevepolitodesign]

Although we no longer have a system executable, we should still account for this in the application template. We already do this for Node version:

suspenders/lib/install/web.rb

Lines 14 to 24 in efe875c

	if node_not_installed? || node_version_unsupported?
	message = <<~ERROR
	=== Node version unsupported ===
	Suspenders requires Node >= 20.0.0
	ERROR
	fail Rails::Generators::Error, message
	end