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

@@ -879,9 +879,13 @@ class Env(object):
 
 
     def __init__(self, path: Path, base: Optional[Path] = None) -> None:
     def __init__(self, path: Path, base: Optional[Path] = None) -> None:
         self._is_windows = sys.platform == "win32"
         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
         self._path = path
-        bin_dir = "bin" if not self._is_windows else "Scripts"
         self._bin_dir = self._path / bin_dir
         self._bin_dir = self._path / bin_dir
 
 
         self._base = base or path
         self._base = base or path