Remove incorrect assertion for Anaconda interpreters (#2856)

* Remove incorrect assertion

* Fix comment

* One more comment rewrite

* Add a newsfragment

newsfragments/2855.bugfix.rst

@@ -0,0 +1 @@
+Don't crash on import in Anaconda interpreters.

trio/_subprocess.py

@@ -50,8 +50,14 @@ def pidfd_open(fd: int, flags: int) -> int:
         from os import pidfd_open
     except ImportError:
         if sys.platform == "linux":
-            # This workaround is only needed on 3.8 and pypy
-            assert sys.version_info < (3, 9) or sys.implementation.name != "cpython"
+            # this workaround is needed on:
+            #  - CPython <= 3.8
+            #  - non-CPython (maybe?)
+            #  - Anaconda's interpreter (as it is built to assume an older
+            #    than current linux kernel)
+            #
+            # The last point implies that other custom builds might not work;
+            # therefore, no assertion should be here.
             import ctypes
 
             _cdll_for_pidfd_open = ctypes.CDLL(None, use_errno=True)