Work around pip-tools conflict with pip 22

Restrict pip to <22 for now until
jazzband/pip-tools#1558 is fixed.

Makefile

@@ -2,7 +2,7 @@
 # which is normally not allowed to appear in a hashed dependency file.
 .PHONY: update-deps
 update-deps:
-	pip install --upgrade pip-tools pip setuptools
+	pip install --upgrade pip-tools 'pip<22' setuptools
 	pip-compile --upgrade --build-isolation --allow-unsafe --generate-hashes --output-file requirements/main.txt requirements/main.in
 	pip-compile --upgrade --build-isolation --allow-unsafe --generate-hashes --output-file requirements/dev.txt requirements/dev.in