Merge global environment variables when merging tasks

internal/taskfile/merge.go

@@ -35,6 +35,13 @@ func Merge(t1, t2 *Taskfile, namespaces ...string) error {
 		t1.Vars[k] = v
 	}
 
+	if t1.Env == nil {
+		t1.Env = make(Vars)
+	}
+	for k, v := range t2.Vars {
+		t1.Env[k] = v
+	}
+
 	if t1.Tasks == nil {
 		t1.Tasks = make(Tasks)
 	}