tests: blame: fix conversion specifiers in format string

While the blame helper function `hunk_message` accepts a printf-style
format string, we didn't add a compiler attribute to let the compiler
check for correct conversion specifiers. As a result, some users of the
function used wrong specifiers.

Add the GIT_FORMAT_PRINTF attribute to the function and fix resulting
warnings by using the correct specifiers.

tests/blame/blame_helpers.c

@@ -31,13 +31,13 @@ void check_blame_hunk_index(git_repository *repo, git_blame *blame, int idx,
 	}
 
 	if (hunk->final_start_line_number != start_line) {
-		hunk_message(idx, hunk, "mismatched start line number: expected %d, got %d",
+		hunk_message(idx, hunk, "mismatched start line number: expected %"PRIuZ", got %"PRIuZ,
 				start_line, hunk->final_start_line_number);
 	}
 	cl_assert_equal_i(hunk->final_start_line_number, start_line);
 
 	if (hunk->lines_in_hunk != len) {
-		hunk_message(idx, hunk, "mismatched line count: expected %d, got %d",
+		hunk_message(idx, hunk, "mismatched line count: expected %"PRIuZ", got %"PRIuZ,
 				len, hunk->lines_in_hunk);
 	}
 	cl_assert_equal_i(hunk->lines_in_hunk, len);

tests/blame/blame_helpers.h

 #include "clar_libgit2.h"
 #include "blame.h"
 
-void hunk_message(size_t idx, const git_blame_hunk *hunk, const char *fmt, ...);
+void hunk_message(size_t idx, const git_blame_hunk *hunk, const char *fmt, ...) GIT_FORMAT_PRINTF(3, 4);
 
 void check_blame_hunk_index(
 		git_repository *repo,