vim-patch:9.0.1990: strange error number

Problem:  strange error number
Solution: change error number,
          add doc tag for E1507

closes: vim/vim#13270

ea746f9e86

Co-authored-by: Christ van Willegen <cvwillegen@gmail.com>

runtime/lua/vim/_meta/vimfn.lua

@@ -6290,6 +6290,13 @@ function vim.fn.prevnonblank(lnum) end
 --- <  E1505: Invalid format specifier:
 ---   %1$d at width %2$d is: %01$*2$.3$d
 ---
+---           *E1507*
+--- This internal error indicates that the logic to
+--- parse a positional format error ran into a problem
+--- that couldn't be otherwise reported. Please file a
+--- bug against vim if you run into this, copying the
+--- exact format string and parameters that were used.
+---
 --- @param fmt any
 --- @param expr1? any
 --- @return any