patch 8.2.0967: unnecessary type casts for vim_strnsave()

Problem:    Unnecessary type casts for vim_strnsave().
Solution:   Remove the type casts.
diff --git a/src/if_ruby.c b/src/if_ruby.c
index 2480ee4..692af4c 100644
--- a/src/if_ruby.c
+++ b/src/if_ruby.c
@@ -1858,7 +1858,7 @@
 
 		rettv->v_type = VAR_STRING;
 		rettv->vval.v_string = vim_strnsave((char_u *)RSTRING_PTR(str),
-							 (int)RSTRING_LEN(str));
+							     RSTRING_LEN(str));
 	    }
 	    break;
 	case T_ARRAY: