Bump fake_ftp to ~> 0.3.0 & adjust tests

Sadly, fake_ftp is unmaintained since 2021, but all other alternatives haven't
been touched for even longer :-/

test/unit/plugins/pushes/ftp/adapter_test.rb

@@ -77,7 +77,7 @@ describe VagrantPlugins::FTPPush::FTPAdapter do
         ftp.upload("#{@dir}/file", "/file")
       end
 
-      expect(server.files).to include("file")
+      expect(server.files).to include("/file")
     end
 
     it "uploads in passive mode" do
@@ -86,7 +86,7 @@ describe VagrantPlugins::FTPPush::FTPAdapter do
         ftp.upload("#{@dir}/file", "/file")
       end
 
-      expect(server.file("file")).to be_passive
+      expect(server.file("/file")).to be_passive
     end
   end
 end

test/unit/plugins/pushes/ftp/push_test.rb

@@ -70,7 +70,7 @@ describe VagrantPlugins::FTPPush::Push do
 
     it "pushes the files to the server" do
       subject.push
-      expect(server.files).to eq(%w(Gemfile data.txt))
+      expect(server.files).to eq(%w[/var/www/site/Gemfile /var/www/site/data.txt])
     end
 
     it "raises informative exception when too many files to process" do

vagrant.gemspec

@@ -47,7 +47,7 @@ Gem::Specification.new do |s|
   s.add_development_dependency "rake", "~> 13.0"
   s.add_development_dependency "rspec", "~> 3.11.0"
   s.add_development_dependency "rspec-its", "~> 1.3.0"
-  s.add_development_dependency "fake_ftp", "~> 0.1.1"
+  s.add_development_dependency "fake_ftp", "~> 0.3.0"
   s.add_development_dependency "webrick", "~> 1.7.0"
 
   # The following block of code determines the files that should be included