gh-101992: update plistlib examples to be runnable (GH-101994)

* gh-101992: update plistlib examples to be runnable

* Update Doc/library/plistlib.rst

---------

(cherry picked from commit a1723ca)

Co-authored-by: Dustin Rodrigues <dust.rod@gmail.com>
Co-authored-by: Terry Jan Reedy <tjreedy@udel.edu>

Doc/library/plistlib.rst

@@ -159,6 +159,9 @@ Examples
 
 Generating a plist::
 
+    import datetime
+    import plistlib
+
     pl = dict(
         aString = "Doodah",
         aList = ["A", "B", 12, 32.1, [1, 2, 3]],
@@ -172,13 +175,19 @@ Generating a plist::
         ),
         someData = b"<binary gunk>",
         someMoreData = b"<lots of binary gunk>" * 10,
-        aDate = datetime.datetime.fromtimestamp(time.mktime(time.gmtime())),
+        aDate = datetime.datetime.now()
     )
-    with open(fileName, 'wb') as fp:
-        dump(pl, fp)
+    print(plistlib.dumps(pl).decode())
 
 Parsing a plist::
 
-    with open(fileName, 'rb') as fp:
-        pl = load(fp)
-    print(pl["aKey"])
+    import plistlib
+
+    plist = b"""<plist version="1.0">
+    <dict>
+        <key>foo</key>
+        <string>bar</string>
+    </dict>
+    </plist>"""
+    pl = plistlib.loads(plist)
+    print(pl["foo"])