bees: fix build by pinning linuxHeaders_5_19

Without the change build fails as:

    ...-linux-headers-6.0/include/linux/fiemap.h:37:30:
      error: flexible array member 'fiemap::fm_extents' not at end of 'struct crucible::Fiemap'
       37 |         struct fiemap_extent fm_extents[]; /* array of mapped extents (out) */
          |                              ^~~~~~~~~~

Upstream ported to the new version but did not release compatible
version yet. As patch backport is a bit convoluted let's wait
for a new release and pin to previous linuxHeaders_5_19 version.

ZHF: https://github.com/NixOS/nixpkgs/issues/199919

pkgs/tools/filesystems/bees/default.nix

@@ -5,6 +5,7 @@
 , bash
 , btrfs-progs
 , coreutils
+, linuxHeaders_5_19
 , python3Packages
 , util-linux
 , nixosTests
@@ -24,6 +25,10 @@ let
     };
 
     buildInputs = [
+      # Works around build failure for flexible array members.
+      # Can be removed after 0.7.3 release where it was fixed upstream.
+      linuxHeaders_5_19
+
       btrfs-progs # for btrfs/ioctl.h
       util-linux # for uuid.h
     ];