kernel: Add test for 5.4

nixos/tests/kernel-generic.nix

@@ -25,6 +25,7 @@ let
   }));
 in
 with pkgs; {
+  linux_5_4 = makeKernelTest "5.4" linuxPackages_5_4;
   linux_5_10 = makeKernelTest "5.10" linuxPackages_5_10;
   linux_5_11 = makeKernelTest "5.11" linuxPackages_5_11;
 }

pkgs/os-specific/linux/kernel/linux-5.4.nix

@@ -1,4 +1,4 @@
-{ lib, buildPackages, fetchurl, perl, buildLinux, modDirVersionArg ? null, ... } @ args:
+{ lib, buildPackages, fetchurl, perl, buildLinux, nixosTests, modDirVersionArg ? null, ... } @ args:
 
 with lib;
 
@@ -15,4 +15,6 @@ buildLinux (args // rec {
     url = "mirror://kernel/linux/kernel/v5.x/linux-${version}.tar.xz";
     sha256 = "1vmpc6yrr2zm4m3naflwik5111jr8hy0mnyddwk31l0p4xbg8smc";
   };
+
+  kernelTests = args.kernelTests or [ nixosTests.kernel-generic.linux_5_4 ];
 } // (args.argsOverride or {}))