Makefile: avoid tox --parallel unless multi=1 is defined
This seems like it was the result of an incorrect merge.
@@ -39,7 +39,6 @@ NUM_JOBS := $(shell printf %s "$(DASH_J)" | sed -e 's/-j//')
TESTCMD ?= $(PYTEST)
BENCHMARKCMD ?= $(BENCHMARK)
TOXCMD ?= $(TOX)
-TOXCMD += --parallel $(NUM_JOBS)
TOXCMD += --develop --skip-missing-interpreters
ifdef multi
TOXCMD += --parallel $(NUM_JOBS)
