utils/envs: fix envs in MSYS2 always broken

Fixes #2867, the virtual environment found seems to be broken
messages when running in MSYS2. This change detects when in MSYS2
in order to use the bin directory for the virtualenv instead of
Scripts which is normally used in Windows.

poetry/utils/env.py

@@ -22,6 +22,7 @@
 from typing import Union
 
 import packaging.tags
+import sysconfig
 import tomlkit
 import virtualenv
 
@@ -879,9 +880,13 @@ class Env(object):
 
     def __init__(self, path: Path, base: Optional[Path] = None) -> None:
         self._is_windows = sys.platform == "win32"
+        self._is_mingw = sysconfig.get_platform() == "mingw"
 
+        if not self._is_windows or self._is_mingw:
+            bin_dir = "bin"
+        else:
+            bin_dir = "Scripts"
         self._path = path
-        bin_dir = "bin" if not self._is_windows else "Scripts"
         self._bin_dir = self._path / bin_dir
 
         self._base = base or path