Fix typo

Cut and paste error.

Signed-off-by: Harumi Kuno <[email protected]>

Author: hkuno

sphinx/writers/manpage.py

@@ -115,7 +115,7 @@ def header(self) -> str:
                 " \"%(date)s\" \"%(version)s\" \"%(manual_group)s\"\n"
                 ".SH NAME\n")
         if self._docinfo['subtitle']:
-                "%(title)s \\- %(subtitle)s\n")
+                tmpl += "%(title)s \\- %(subtitle)s\n"
         return tmpl % self._docinfo
 
     def visit_start_of_file(self, node: Element) -> None: