shared/microhttp-util: silence gcc warning

shared/microhttp-util: silence gcc warning

../src/journal-remote/microhttpd-util.c: In function ‘check_permissions’:
../src/journal-remote/microhttpd-util.c:301:5: error: function might be candidate for attribute ‘noreturn’ [-Werror=suggest-attribute=noreturn]
  301 | int check_permissions(struct MHD_Connection *connection, int *code, char **hostname) {
      |     ^~~~~~~~~~~~~~~~~
cc1: all warnings being treated as errors

Fixes #23630.