Fix missing branch on tox.ini config

Here we use a specific SHA that we now is "green" to avoid problems with
a moving HEAD.

Author: abravalheri

tox.ini

@@ -1,8 +1,8 @@
 [testenv]
 deps =
 	# Ideally all the dependencies should be set as "extras"
-	# workaround for pypa/build#630
-	build[virtualenv] @ git+https://github.com/jaraco/build@bugfix/630-importlib-metadata
+	build[virtualenv] @ git+https://github.com/pypa/build@59c1f87
+	# ^-- pypa/build#630, use dev version while we wait for the new release
 setenv =
 	PYTHONWARNDEFAULTENCODING = 1
 	SETUPTOOLS_ENFORCE_DEPRECATION = 1