bracken: fix installation

[V-Karch]

Without this fix, I was getting the following error when attempting to install bracken:

==> No patches needed for bracken    
==> bracken: Executing phase: 'install'
==> [2026-05-14-11:01:09.210554] /usr/bin/chmod +x ./install_bracken.sh
==> [2026-05-14-11:01:09.212286] ./install_bracken.sh /dev/shm/spack.vfk4083/stage/spack-stage-bracken-2.9-4nvwbrobkznzjzgqw7o7qwjd6uqip6mb/spack-src
make: *** internal error: invalid --jobserver-auth string 'fifo:/tmp/tmpgwct33q6/jobserver_fifo'.  Stop.
Traceback (most recent call last):                  
  File "/home/vfk4083/spackng/spack/lib/spack/spack/new_installer.py", line 542, in worker_function
    _install(                           
  File "/home/vfk4083/spackng/spack/lib/spack/spack/new_installer.py", line 772, in _install
    phase.execute()
  File "/home/vfk4083/spackng/spack/lib/spack/spack/builder.py", line 382, in execute
    self.phase_fn(pkg, pkg.spec, pkg.prefix)
  File "/home/vfk4083/spackng/spack/lib/spack/spack/builder.py", line 254, in _adapter
    return phase_fn(spec, prefix)                                                                                                                            
  File "/home/vfk4083/spackng/spack-packages/repos/spack_repo/builtin/packages/bracken/package.py", line 37, in install
    installer(self.stage.source_path)
  File "/home/vfk4083/spackng/spack/lib/spack/spack/util/executable.py", line 322, in __call__
    raise ProcessError(f"Command exited with status {proc.returncode}:", long_msg)
spack.util.executable.ProcessError: Command exited with status 2:
    ./install_bracken.sh /dev/shm/spack.vfk4083/stage/spack-stage-bracken-2.9-4nvwbrobkznzjzgqw7o7qwjd6uqip6mb/spack-src

I figured I should try clearing the MAKEFLAGS before installing and that did seem to fix it