gh-161077: Replace "truthy"/"falsy" with "true"/"false" in the docs

Python's documented terminology is true/false, not truthy/falsy, as used
by Truth Value Testing, Boolean Operations, and the if and while
statements. This replaces the five remaining occurrences in Doc/.

In tkinter, TRUE/YES/ON are the integer 1 rather than the True
singleton, so those two lines are phrased to keep true/false lowercase
and unstyled instead of starting the sentence with a capitalised "True".

Supersedes the retracted PR gh-158663.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Author: Viltrumlik

Doc/builtins/functions.rst

@@ -1950,7 +1950,7 @@ are always available.  They are listed here in alphabetical order.
       >>> MISSING
       <MISSING>
 
-   Sentinel objects are truthy and compare equal only to themselves.  They are
+   Sentinel objects are true and compare equal only to themselves.  They are
    intended to be compared with the :keyword:`is` operator.
 
    ``sentinel`` does not support subclassing.

Doc/library/smtplib.rst

@@ -24,7 +24,7 @@ Protocol) and :rfc:`1869` (SMTP Service Extensions).
    An :class:`SMTP` instance encapsulates an SMTP connection.  It has methods
    that support a full repertoire of SMTP and ESMTP operations.
 
-   If the host parameter is set to a truthy value, :meth:`SMTP.connect` is called with
+   If the host parameter is set to a true value, :meth:`SMTP.connect` is called with
    host and port automatically when the object is created; otherwise, :meth:`!connect` must
    be called manually.
 
@@ -88,7 +88,7 @@ Protocol) and :rfc:`1869` (SMTP Service Extensions).
    required from the beginning of the connection and using :meth:`SMTP.starttls` is
    not appropriate.
 
-   If the host parameter is set to a truthy value, :meth:`SMTP.connect` is called with host
+   If the host parameter is set to a true value, :meth:`SMTP.connect` is called with host
    and port automatically when the object is created; otherwise, :meth:`!SMTP.connect` must
    be called manually.
 

Doc/library/tkinter.rst

@@ -6820,13 +6820,13 @@ and :mod:`!tkinter.constants` namespaces.
           YES
           ON
 
-   Truthy values, all equal to the integer ``1``.
+   Values that are true, all equal to the integer ``1``.
 
 .. data:: FALSE
           NO
           OFF
 
-   Falsy values, all equal to the integer ``0``.
+   Values that are false, all equal to the integer ``0``.
 
 .. data:: N
           S