Issue #15340: Fix importing the random module when /dev/urandom cannot be opened.

This was a regression caused by the hash randomization patch.

Misc/NEWS

@@ -103,6 +103,9 @@ Core and Builtins
 Library
 -------
 
+- Issue #15340: Fix importing the random module when /dev/urandom cannot
+  be opened.  This was a regression caused by the hash randomization patch.
+
 - Issue #15841: The readable(), writable() and seekable() methods of
   io.BytesIO and io.StringIO objects now raise ValueError when the object has
   been closed.  Patch by Alessandro Moura.

Python/random.c

@@ -165,7 +165,8 @@ dev_urandom_python(char *buffer, Py_ssize_t size)
     Py_END_ALLOW_THREADS
     if (fd < 0)
     {
-        PyErr_SetFromErrnoWithFilename(PyExc_OSError, "/dev/urandom");
+        PyErr_SetString(PyExc_NotImplementedError,
+                        "/dev/urandom (or equivalent) not found");
         return -1;
     }