Suppress syntax warnings on Python 3.12.

Python 3.12 has a new warning for backslash-character pairs that are not
valid escape sequences at the level of string literals, as opposed to in
some interior syntax such as regular expressions
(https://docs.python.org/3/whatsnew/3.12.html#other-language-changes).
Suppress it by using raw strings.

contrib/kh2reg.py

@@ -27,7 +27,7 @@ def winmungestr(s):
     candot = 0
     r = ""
     for c in s:
-        if c in ' \*?%~' or ord(c)<ord(' ') or (c == '.' and not candot):
+        if c in r' \*?%~' or ord(c)<ord(' ') or (c == '.' and not candot):
             r = r + ("%%%02X" % ord(c))
         else:
             r = r + c
@@ -385,7 +385,7 @@ class OutputFormatter(object):
 class WindowsOutputFormatter(OutputFormatter):
     def header(self):
         # Output REG file header.
-        self.fh.write("""REGEDIT4
+        self.fh.write(r"""REGEDIT4
 
 [HKEY_CURRENT_USER\Software\SimonTatham\PuTTY\SshHostKeys]
 """)

test/testcrypt.py

@@ -308,8 +308,8 @@ def _lex_testcrypt_header(header):
         # And then match a token
         '({})'.format('|'.join((
             # Punctuation
-            '\(',
-            '\)',
+            r'\(',
+            r'\)',
             ',',
             # Identifier
             '[A-Za-z_][A-Za-z0-9_]*',