pip is not needed to run tests.

--- build-1.6.1/pyproject.toml.orig
+++ build-1.6.1/pyproject.toml
@@ -102,7 +102,6 @@
   'setuptools >= 56.0.0; python_version == "3.11"',
   'setuptools >= 67.8.0; python_version >= "3.12"',
   "setuptools_scm >= 6.4.2",
-  "pip >= 22.3",
   { include-group = "test-core" },
   { include-group = "extra" },
 ]