vim-patch:9.1.1318: tests: test_format fails

Problem:  tests: test_format fails (after 9.1.1314).
Solution: Increase the string size.  Add missing test_format.res in
          NEW_TESTS_RES (zeertzjq).

closes: vim/vim#17144

e9a27ef373

src/nvim/eval.lua

@@ -8169,7 +8169,8 @@ M.funcs = {
       <      1.41
 
       You will get an overflow error |E1510|, when the field-width
-      or precision will result in a string longer than 6400 chars.
+      or precision will result in a string longer than 1 MB
+      (1024*1024 = 1048576) chars.
 
       					*E1500*
       You cannot mix positional and non-positional arguments: >vim