patch 9.0.1930: compiler warnings with clang-17

Problem:  compiler warnings with clang-17
Solution: Fix function prototypes and function pointer

fix: clang compilation warnings with -Wstrict-prototypes

Change fixes this kind of compilation warnings with clang:
```
proto/if_python3.pro:13:20: warning: a function declaration without a prototype is deprecated in all versions of C [-Wstrict-prototypes]
   13 | int python3_version();
      |                    ^
      |                     void
```

closes: #13166

Signed-off-by: Christian Brabandt <cb@256bit.org>
Co-authored-by: Dominique Pellé <dominique.pelle@tomtom.com>
diff --git a/src/proto/if_python3.pro b/src/proto/if_python3.pro
index d2bcd8c..0e139b9 100644
--- a/src/proto/if_python3.pro
+++ b/src/proto/if_python3.pro
@@ -10,5 +10,5 @@
 void python3_tabpage_free(tabpage_T *tab);
 void do_py3eval(char_u *str, typval_T *rettv);
 int set_ref_in_python3(int copyID);
-int python3_version();
+int python3_version(void);
 /* vim: set ft=c : */