Update because run output is now a struct

The tests that use `fetch_supported_git_protocol` haven't
been running for a while, so when `run` output was changed
from a string to a struct, the method wasn't update because
nothing was using it.

qa/qa/git/repository.rb

@@ -165,7 +165,7 @@ module QA
         # ls-remote is one command known to respond to Git protocol v2 so we use
         # it to get output including the version reported via Git tracing
         output = run("git ls-remote #{uri}", "GIT_TRACE_PACKET=1")
-        output[/git< version (\d+)/, 1] || 'unknown'
+        output.response[/git< version (\d+)/, 1] || 'unknown'
       end
 
       def try_add_credentials_to_netrc

qa/spec/git/repository_spec.rb

@@ -69,18 +69,20 @@ describe QA::Git::Repository do
     end
 
     describe '#fetch_supported_git_protocol' do
+      Result = Struct.new(:response)
+
       it "reports the detected version" do
-        expect(repository).to receive(:run).and_return("packet: git< version 2")
+        expect(repository).to receive(:run).and_return(Result.new("packet: git< version 2"))
         expect(repository.fetch_supported_git_protocol).to eq('2')
       end
 
       it 'reports unknown if version is unknown' do
-        expect(repository).to receive(:run).and_return("packet: git< version -1")
+        expect(repository).to receive(:run).and_return(Result.new("packet: git< version -1"))
         expect(repository.fetch_supported_git_protocol).to eq('unknown')
       end
 
       it 'reports unknown if content does not identify a version' do
-        expect(repository).to receive(:run).and_return("foo")
+        expect(repository).to receive(:run).and_return(Result.new("foo"))
         expect(repository.fetch_supported_git_protocol).to eq('unknown')
       end
     end