rt-tests: 2.8 -> 2.9, fix build w/ glibc-2.42

Failing Hydra build: https://hydra.nixos.org/build/317799900

This turns of a warning about a potential format overflow, but I
consider it sufficiently unlikely to have enough threads[1] such that
this actually causes an overflow.

[1] https://git.kernel.org/pub/scm/utils/rt-tests/rt-tests.git/tree/src/pmqtest/pmqtest.c#n546

pkgs/by-name/rt/rt-tests/package.nix

@@ -9,13 +9,15 @@
 
 stdenv.mkDerivation rec {
   pname = "rt-tests";
-  version = "2.8";
+  version = "2.9";
 
   src = fetchurl {
     url = "https://git.kernel.org/pub/scm/utils/rt-tests/rt-tests.git/snapshot/${pname}-${version}.tar.gz";
-    sha256 = "sha256-iBpd7K9VpvUH5wXBKypyQl8NAHN3Om5/PcoJ8RH37mI=";
+    sha256 = "sha256-Zmb0RqGvS4bHy+6Krs3of1WUWOqJMOH0FHAXIqlteys=";
   };
 
+  env.NIX_CFLAGS_COMPILE = "-Wno-error=format-overflow";
+
   nativeBuildInputs = [ makeWrapper ];
   buildInputs = [
     numactl