Switch from pep517 lib to build CLI

This is necessary because `pep517` is going to drop its experimental
CLIs eventually and the PyPA recomments using a new tool called
`build` instead. `pypa/build` is a CLI built around the APIs provided
by the `pep517` library.

Refs:
* pypa/pyproject-hooks#83
* pypa/pyproject-hooks#91

.github/workflows/build-test-n-publish.yml

@@ -172,7 +172,7 @@ jobs:
     env:
       ANSIBLE_PYLIBSSH_TRACING: >-
         ${{ fromJSON(needs.pre-setup.outputs.profiling_enabled) && 1 || 0 }}
-      PEP517_ARGS: --binary
+      PEP517_BUILD_ARGS: --binary
       PY_COLORS: 1
       TOXENV: build-wheels-pip,delocate-macos-wheels,metadata-validation
       TOX_PARALLEL_NO_SPINNER: 1
@@ -580,7 +580,7 @@ jobs:
     env:
       ANSIBLE_PYLIBSSH_TRACING: >-
         ${{ fromJSON(needs.pre-setup.outputs.profiling_enabled) && 1 || 0 }}
-      PEP517_ARGS: --source
+      PEP517_BUILD_ARGS: --source
       PY_COLORS: 1
       TOXENV: build-dists,metadata-validation
       TOX_PARALLEL_NO_SPINNER: 1

tox.ini

@@ -1,6 +1,6 @@
 [tox]
 envlist = python
-minversion = 3.19.0
+minversion = 3.21.0
 requires =
     setuptools >= 40.9.0
     pip >= 19.0.3
@@ -91,7 +91,7 @@ setenv =
 [dists]
 setenv =
     {[testenv]setenv}
-    PEP517_OUT_DIR = {env:PEP517_OUT_DIR:{toxinidir}/dist}
+    PEP517_OUT_DIR = {env:PEP517_OUT_DIR:{toxinidir}{/}dist}
 
 
 [testenv:cleanup-dists]
@@ -118,18 +118,16 @@ isolated_build = true
 usedevelop = false
 skip_install = true
 deps =
-    # NOTE: v0.7.0 added support for backend-path in pyproject.toml but
-    # NOTE: why not use something newer if we can?
-    pep517 >= 0.8.2
+    build >= 0.3.1, < 0.4.0
 passenv =
-    PEP517_ARGS
+    PEP517_BUILD_ARGS
 setenv =
     {[dists]setenv}
 commands =
-    {envpython} -m pep517.build \
-      {env:PEP517_ARGS:--source --binary} \
-      --out-dir {env:PEP517_OUT_DIR} \
-      {toxinidir}
+    {envpython} -m build \
+      --outdir '{env:PEP517_OUT_DIR}{/}' \
+      {posargs:{env:PEP517_BUILD_ARGS:--sdist --wheel}} \
+      '{toxinidir}'
 
 
 [testenv:build-wheels-pip]