Remove upgrade of packages from pip install

The new pip (24.3) has problems with older packages. Errors of the form
```
AttributeError: 'InstallRequirement' object has no attribute 'use_pep517'
```
That are unfixable from the user side.

Author: steve-downey

Makefile

@@ -143,7 +143,7 @@ requirements-dev.txt: requirements-dev.in
 
 $(VENV):
 	$(PYEXECPATH) -m venv $(VENV)
-	$(PIP) install --upgrade pip setuptools wheel
+	$(PIP) install pip setuptools wheel
 	$(PIP) install pip-tools
 
 $(VENV)/$(MARKER): requirements.txt requirements-dev.txt | $(VENV)