procutil: move stdin assignment outside of try-finally block stable

procutil: move stdin assignment outside of try-finally block

There is an stdin variable in the global scope of this module. And in the
`finally` block of this try-finally statement we're checking `if stdin is not
None`.  Let's make sure we don't confuse code check tools into thinking we want
to use global stdin by moving this line of code outside of `try`.

This was caught by pytype 2023.11.21 on Python 3.11.2.

--- a/mercurial/utils/procutil.py	Sat Dec 02 15:02:03 2023 -0300
+++ b/mercurial/utils/procutil.py	Sat Dec 02 15:10:28 2023 -0300
@@ -686,8 +686,9 @@
         # we can't use close_fds *and* redirect stdin. I'm not sure that we
         # need to because the detached process has no console connection.
 
+        stdin = None
+
         try:
-            stdin = None
             if stdin_bytes is not None:
                 stdin = pycompat.unnamedtempfile()
                 stdin.write(stdin_bytes)