fix: Install pip and pip-tools in upgrade script (#165)

Makefile

@@ -55,6 +55,8 @@ upgrade: $(COMMON_CONSTRAINTS_TXT)  ## update the requirements/*.txt files with
 	# Make sure to compile files after any other files they include!
 	pip-compile --upgrade --allow-unsafe --rebuild -o requirements/pip.txt requirements/pip.in
 	pip-compile --upgrade -o requirements/pip-tools.txt requirements/pip-tools.in
+	pip install -qr requirements/pip.txt
+	pip install -qr requirements/pip-tools.txt
 	pip-compile --upgrade -o requirements/base.txt requirements/base.in
 	pip-compile --upgrade -o requirements/test.txt requirements/test.in
 	pip-compile --upgrade -o requirements/doc.txt requirements/doc.in