Ruby 3.3 incompatibility

[glitchinfinity]

Ruby 3.3 removed File.exists and only left File.exist.
PR #15 aims to fix this.

Stack trace:

stdout : ==> 1. Linking scripts directory to '/home/user/agent/workspace/app/repos/repo/user/vendor/ruby/3.3.0/gems/git_bpf-1.0.1/lib/git_bpf'.
stderr : fatal: no such section: gitbpf
/home/user/agent/workspace/app/repos/repo/user/vendor/ruby/3.3.0/gems/git_bpf-1.0.1/lib/git_bpf/commands/init.rb:98:in `execute': undefined method `exists?' for class File (NoMethodError)

    if not File.exists? scripts
               ^^^^^^^^
Did you mean?  exist?
	from /home/user/agent/workspace/app/repos/repo/user/vendor/ruby/3.3.0/gems/git_bpf-1.0.1/lib/git_bpf/lib/gitflow.rb:197:in `block in run'
	from /home/user/agent/workspace/app/repos/repo/user/vendor/ruby/3.3.0/gems/git_bpf-1.0.1/lib/git_bpf/lib/gitflow.rb:183:in `catch'
	from /home/user/agent/workspace/app/repos/repo/user/vendor/ruby/3.3.0/gems/git_bpf-1.0.1/lib/git_bpf/lib/gitflow.rb:183:in `run'
	from /home/user/agent/workspace/app/repos/repo/user/vendor/ruby/3.3.0/gems/git_bpf-1.0.1/bin/git-bpf-init:6:in `block in <top (required)>'
exit   : 1
ERROR: Unable to execute git-bpf-init, perhaps it was already initiated?