Unpin pyserial version for the modes dependencies (#1329)

* Switch to a wider pip reqt for pyserial as we're getting a clash between our ==3.4 version and the >=3.0 for esptool
Mock out some ensure/create calls on venv

* + Tidy-ups

Co-authored-by: Tim Golden <mail@timgolden.me.uk>

Author: carlosperate

mu/wheels/__init__.py

@@ -22,7 +22,7 @@
         "git+https://github.com/mu-editor/pgzero.git@mu-wheel",
     ),
     ("flask", "flask==1.1.2"),
-    ("serial", "pyserial==3.4"),
+    ("serial", "pyserial>=3.0"),
     ("qtconsole", "qtconsole==4.7.4"),
     ("nudatus", "nudatus>=0.0.3"),
     ("esptool", "esptool==3.*"),