[cleanup] use type annotation for singledispatch

The register() attribute supports using type annotations with Python 3.7.
Ignore it for some function, otherwise Union, Tuple, and List must be
imported from typing.

Bug: T347026
Change-Id: I543098278eeb9c4af187b17a4f18dfb12056a78b
---
M pywikibot/date.py
1 file changed, 17 insertions(+), 3 deletions(-)

diff --git a/pywikibot/date.py b/pywikibot/date.py
index 4a85afc..09d7caf 100644
--- a/pywikibot/date.py
+++ b/pywikibot/date.py
@@ -240,7 +240,7 @@
     return lst[value - 1]
 
 
-@slh.register(str)
+@slh.register
 def _(value: str, lst: Sequence[str]) -> int:
     return lst.index(value) + 1
 
@@ -251,7 +251,7 @@
     return dh_constVal(value, 0, match)
 
 
-@dh_singVal.register(str)
+@dh_singVal.register
 def _(value: str, match: str) -> int:
     return dh_constVal(value, 0, match)  # type: ignore[return-value]
 
@@ -268,7 +268,7 @@
     raise ValueError(f'unknown value {value}')
 
 
-@dh_constVal.register(str)
+@dh_constVal.register
 def _(value: str, ind: int, match: str) -> int:
     if value == match:
         return ind

