Fix charm install hook by pinning setuptools (#60)

- pin setuptools to be able to install without errors
- Setuptools 71 will prefer installed dependencies over the
  vendored ones and this is currently breaking the instalation

More details can be found at:
- pypa/setuptools#4483
- pypa/packaging-problems#342

src/wheelhouse.txt

@@ -0,0 +1,2 @@
+# https://github.com/pypa/setuptools/issues/4483
+setuptools==70.0.0