Fix error caused by a bad base_python path

docs/changelog/3105.bugfix.rst

@@ -0,0 +1 @@
+Handle ``FileNotFoundError`` when the ``base_python`` interpreter doesn't exist

src/tox/tox_env/python/virtual_env/api.py

@@ -132,7 +132,7 @@ def _get_python(self, base_python: list[str]) -> PythonInfo | None:  # noqa: ARG
         # the base pythons are injected into the virtualenv_env_vars, so we don't need to use it here
         try:
             interpreter = self.creator.interpreter
-        except RuntimeError:  # if can't find
+        except (FileNotFoundError, RuntimeError):  # Unable to find the interpreter
             return None
         return PythonInfo(
             implementation=interpreter.implementation,

tests/tox_env/python/test_python_api.py

@@ -277,3 +277,10 @@ def test_list_installed_deps_explicit_cli(
         assert "pip==" in result.out
     else:
         assert "pip==" not in result.out
+
+
+def test_usedevelop_with_nonexistent_basepython(tox_project: ToxProjectCreator) -> None:
+    ini = "[testenv]\nusedevelop = true\n[testenv:unused]\nbasepython = /nonexistent/bin/python"
+    project = tox_project({"tox.ini": ini})
+    result = project.run()
+    assert result.code == 0