Reuse package_env with --installpkg (#2803)

Co-authored-by: q0w <43147888+q0w@users.noreply.github.com>

docs/changelog/2442.bugfix.rst

@@ -0,0 +1 @@
+Reuse package_env with ``--installpkg`` - by :user:`q0w`.

src/tox/tox_env/runner.py

@@ -87,9 +87,8 @@ def interrupt(self) -> None:
         self._call_pkg_envs("interrupt")
 
     def get_package_env_types(self) -> tuple[str, str] | None:
-        has_external_pkg = getattr(self.options, "install_pkg", None) is not None
-        if self._register_package_conf() or has_external_pkg:
-            has_external_pkg = has_external_pkg or self.conf["package"] == "external"
+        if self._register_package_conf():
+            has_external_pkg = self.conf["package"] == "external"
             self.core.add_config(
                 keys=["package_env", "isolated_build_env"],
                 of_type=str,

tests/tox_env/python/virtual_env/package/test_package_cmd_builder.py

@@ -147,3 +147,14 @@ def test_tox_install_pkg_bad_wheel(tox_project: ToxProjectCreator, tmp_path: Pat
 
     result.assert_failed()
     assert "failed with no .dist-info inside " in result.out, result.out
+
+
+def test_tox_install_pkg_with_skip_install(
+    tox_project: ToxProjectCreator,
+    demo_pkg_inline: Path,
+    demo_pkg_inline_wheel: Path,
+) -> None:
+    ini = "[testenv:foo]\nskip_install = true"
+    project = tox_project({"tox.ini": ini, "pyproject.toml": (demo_pkg_inline / "pyproject.toml").read_text()})
+    result = project.run("-e", "py", "--installpkg", str(demo_pkg_inline_wheel))
+    result.assert_success()