Formatting of `for T : Type of Container loop` disagrees with GNAT warning

Noticed in this code snippet, autoformat in VS Code results in this:

 function FNV_1A (S : String) return String_Hash is
 begin
    return Value : String_Hash := 14_695_981_039_346_656_037 do
       for C:Character of S loop
          Value := Value xor Character'Pos (C);
          Value := Value * 1099511628211;
       end loop;
    end return;
 end FNV_1A;

This triggers a GNAT warning: (style) space required [-gnatyt] between the C and : of the for loop.

Reproduce the formatting shown for the Ada for C:Character of S loop example in VS Code and compare it with the GNAT style warning. Trace the formatting behavior in gnatformat and make the output include the required spacing between C and :. Confirm that the formatted loop no longer triggers this warning.