Write unit tests with the help of afero

Afero is a package that lets you mock out a filesystem with an in-memory filesystem.
It allows us to easily create the files required for a given test without worrying about
a cleanup step or different tests tripping on eachother when run in parallel.

Later on I'll standardise on using afero over the vanilla os package

pkg/commands/git_commands/file_loader_test.go

@@ -5,7 +5,6 @@ import (
 
 	"github.com/jesseduffield/lazygit/pkg/commands/models"
 	"github.com/jesseduffield/lazygit/pkg/commands/oscommands"
-	"github.com/jesseduffield/lazygit/pkg/utils"
 	"github.com/stretchr/testify/assert"
 )
 
@@ -178,7 +177,7 @@ func TestFileGetStatusFiles(t *testing.T) {
 			cmd := oscommands.NewDummyCmdObjBuilder(s.runner)
 
 			loader := &FileLoader{
-				Common:      utils.NewDummyCommon(),
+				GitCommon:   buildGitCommon(commonDeps{}),
 				cmd:         cmd,
 				config:      &FakeFileLoaderConfig{showUntrackedFiles: "yes"},
 				getFileType: func(string) string { return "file" },