Remove one of the tracebacks from conftest import failures

This removes the KeyError from the traceback chain when an
conftest fails to import:

    return self._conftestpath2mod[key]
    E   KeyError: WindowsPath('D:/projects/pytest/.tmp/root/foo/conftest.py')

    During handling of the above exception, another exception occurred:
    ...
        raise RuntimeError("some error")
    E   RuntimeError: some error

    During handling of the above exception, another exception occurred:
    ...
    E   _pytest.config.ConftestImportFailure: (...)

By slightly changing the code, we can remove the first chain, which is often
very confusing to users and doesn't help with anything.

Fix #7223

src/_pytest/config/__init__.py

@@ -1,5 +1,6 @@
 """ command line options, ini-file and conftest.py processing. """
 import argparse
+import contextlib
 import copy
 import enum
 import inspect
@@ -511,34 +512,36 @@ class PytestPluginManager(PluginManager):
         # Using Path().resolve() is better than py.path.realpath because
         # it resolves to the correct path/drive in case-insensitive file systems (#5792)
         key = Path(str(conftestpath)).resolve()
-        try:
-            return self._conftestpath2mod[key]
-        except KeyError:
-            pkgpath = conftestpath.pypkgpath()
-            if pkgpath is None:
-                _ensure_removed_sysmodule(conftestpath.purebasename)
-            try:
-                mod = conftestpath.pyimport()
-                if (
-                    hasattr(mod, "pytest_plugins")
-                    and self._configured
-                    and not self._using_pyargs
-                ):
-                    _fail_on_non_top_pytest_plugins(conftestpath, self._confcutdir)
-            except Exception:
-                raise ConftestImportFailure(conftestpath, sys.exc_info())
 
-            self._conftest_plugins.add(mod)
-            self._conftestpath2mod[key] = mod
-            dirpath = conftestpath.dirpath()
-            if dirpath in self._dirpath2confmods:
-                for path, mods in self._dirpath2confmods.items():
-                    if path and path.relto(dirpath) or path == dirpath:
-                        assert mod not in mods
-                        mods.append(mod)
-            self.trace("loading conftestmodule {!r}".format(mod))
-            self.consider_conftest(mod)
-            return mod
+        with contextlib.suppress(KeyError):
+            return self._conftestpath2mod[key]
+
+        pkgpath = conftestpath.pypkgpath()
+        if pkgpath is None:
+            _ensure_removed_sysmodule(conftestpath.purebasename)
+
+        try:
+            mod = conftestpath.pyimport()
+            if (
+                hasattr(mod, "pytest_plugins")
+                and self._configured
+                and not self._using_pyargs
+            ):
+                _fail_on_non_top_pytest_plugins(conftestpath, self._confcutdir)
+        except Exception as e:
+            raise ConftestImportFailure(conftestpath, sys.exc_info()) from e
+
+        self._conftest_plugins.add(mod)
+        self._conftestpath2mod[key] = mod
+        dirpath = conftestpath.dirpath()
+        if dirpath in self._dirpath2confmods:
+            for path, mods in self._dirpath2confmods.items():
+                if path and path.relto(dirpath) or path == dirpath:
+                    assert mod not in mods
+                    mods.append(mod)
+        self.trace("loading conftestmodule {!r}".format(mod))
+        self.consider_conftest(mod)
+        return mod
 
     #
     # API for bootstrapping plugin loading