fix: set process working dir based on relative path of -f file too

Why
===
* extends now sets the working dir of the processes in it based on the
relative path of the process-compose file.
* The documentation says that -f should be equvalent to using extends
* However, -f does not set the workign dir of the process to match the
process-compose file's path
* To make the documentation consistent again, we should also set the
working dir for the -f filename case.

What changed
===
* Move the working dir copy from loadExtendProject to
loadProjectFromFile

Test plan
===
* -f and extends both set the expected working dir of the processes in
my local tests

src/loader/loader.go

@@ -93,7 +93,6 @@ func loadExtendProject(p *types.Project, opts *LoaderOptions, file string, index
 			log.Error().Err(err).Msgf("Failed to load the extend project %s", p.ExtendsProject)
 			return fmt.Errorf("failed to load extend project %s: %w", p.ExtendsProject, err)
 		}
-		copyWorkingDirToProcesses(project, filepath.Dir(p.ExtendsProject))
 		opts.projects = slices.Insert(opts.projects, index, project)
 		err = loadExtendProject(project, opts, p.ExtendsProject, index)
 		if err != nil {
@@ -161,6 +160,7 @@ func loadProjectFromFile(inputFile string, opts *LoaderOptions) (*types.Project,
 		}
 	}
 
+	copyWorkingDirToProcesses(project, filepath.Dir(inputFile))
 	log.Info().Msgf("Loaded project from %s", inputFile)
 	return project, nil
 }

src/loader/loader_test.go

@@ -177,8 +177,8 @@ func TestLoadFileWithExtendProject(t *testing.T) {
 		}
 	}
 	for _, proc := range opts.projects[1].Processes {
-		if proc.WorkingDir != "" {
-			t.Errorf("expected empty, got %s", proc.WorkingDir)
+		if proc.WorkingDir != expected {
+			t.Errorf("expected %s, got %s", expected, proc.WorkingDir)
 		}
 	}
 }