Fix restarting with locked version when $PROGRAM_NAME has been changed

Use Process.argv0 instead of $PROGRAM_NAME because $PROGRAM_NAME is
liable to be changed but Process.argv0 is not.

bundler/lib/bundler/self_manager.rb

@@ -84,8 +84,8 @@ def restart_with(version)
         require "shellwords"
         cmd = [*Shellwords.shellsplit(bundler_spec_original_cmd), *ARGV]
       else
-        cmd = [$PROGRAM_NAME, *ARGV]
-        cmd.unshift(Gem.ruby) unless File.executable?($PROGRAM_NAME)
+        cmd = [Process.argv0, *ARGV]
+        cmd.unshift(Gem.ruby) unless File.executable?(Process.argv0)
       end
 
       Bundler.with_original_env do

bundler/spec/runtime/self_management_spec.rb

@@ -194,6 +194,25 @@
       expect(out).to include("Using bundler #{Bundler::VERSION}")
     end
 
+    it "uses the right original script when re-execing, even if `$0` has been changed", :ruby_repo do
+      bundle "config path vendor/bundle"
+
+      system_gems "bundler-9.9.9", path: vendored_gems
+
+      test = bundled_app("test.rb")
+
+      create_file test, <<~RUBY
+        $0 = "this is the program name"
+        require "bundler/setup"
+      RUBY
+
+      lockfile_bundled_with("9.9.9")
+
+      sys_exec "#{Gem.ruby} #{test}", artifice: nil, raise_on_error: false
+      expect(err).to include("Could not find myrack-1.0.0")
+      expect(err).not_to include("this is the program name")
+    end
+
     private
 
     def lockfile_bundled_with(version)