Merge remote-tracking branch 'upstream/master' into makefile-tweaks

py/objset.c

py/objstr.c

tests/basics/iter-of-iter.py

tests/basics/set1.py

tests/basics/set_binop.py

tests/basics/set_symmetric_difference.py

tests/basics/set_union.py

tests/basics/string_replace.py

tools/pip-micropython