gnu: python-importlib-resources: Update to 5.12.0.

* gnu/packages/python-xyz.scm (python-importlib-resources): Update to 5.12.0.
[build-system]: Use pyproject-build-system.
[arguments]: Add phase to avoid "pip install".
[native-inputs]: Remove python-toml; add python-flake8, python-pytest,
python-pytest-black, python-pytest-checkdocs, python-pytest-cov,
python-pytest-enabler, python-pytest-flake8, python-pytest-mypy, and
python-setuptools-57.
[propagated-inputs]: Add python-zipp.

gnu/packages/python-xyz.scm

@@ -8932,15 +8932,53 @@ older Python versions.")
 (define-public python-importlib-resources
   (package
     (name "python-importlib-resources")
-    (version "3.0.0")
+    (version "5.12.0")
     (source (origin
               (method url-fetch)
               (uri (pypi-uri "importlib_resources" version))
               (sha256
                (base32
-                "1hq626mx5jl9zfl0wdrjkxsnh8qd98fqv322n68b9251xjk4bxqr"))))
-    (build-system python-build-system)
-    (native-inputs (list python-setuptools-scm python-toml))
+                "1xi2ggdfdj1bg7w728lvy6j3rjqhklalaanzmscpj7awpy4jbs2b"))))
+    (build-system pyproject-build-system)
+    (arguments
+     (list
+      #:phases
+      '(modify-phases %standard-phases
+         ;; The build system insists on ignoring the existing environment and
+         ;; running "pip install".
+         (add-after 'unpack 'do-not-use-pip-install
+           (lambda _
+             (substitute* "pyproject.toml"
+               (("^build-backend.*") "\
+build-backend = \"backend\"
+backend_path = [\"_custom_build\"]\n")
+               (("requires = .*") "requires = []\n"))
+             (mkdir-p "_custom_build")
+             (with-output-to-file "_custom_build/backend.py"
+               (lambda _
+                 (display "\
+from setuptools import build_meta as _orig
+from setuptools.build_meta import *
+def get_requires_for_build_wheel(config_settings=None):
+    return []
+def get_requires_for_build_sdist(config_settings=None):
+    return []
+")))
+             (setenv "PYTHONPATH"
+                     (string-append (getcwd) "/_custom_build")))))))
+    (native-inputs
+     (list python-flake8
+           python-pytest
+           python-pytest-black
+           python-pytest-checkdocs
+           python-pytest-cov
+           python-pytest-enabler
+           python-pytest-flake8
+           python-pytest-mypy
+           python-setuptools-57
+           python-setuptools-scm))
+    (propagated-inputs
+     (list python-zipp))
     (home-page "https://importlib-resources.readthedocs.io/")
     (synopsis "Read resources from Python packages")
     (description