Allow @ in quoted string token

[bachradsusi]

Fixes:

base-policy/policy/modules/system/systemd.te:1400: (F): syntax error, unexpected UNKNOWN_TOKEN (F-001)
 1400 | filetrans_pattern(systemd_zram_generator_t, systemd_unit_file_t, systemd_zram_generator_unit_file_t, dir, "systemd-zram-setup@zram0.service.d")
      |                                                                                                           ^
base-policy/policy/modules/system/systemd.te:1400: (F): Error: Invalid statement (F-001)
 1400 | filetrans_pattern(systemd_zram_generator_t, systemd_unit_file_t, systemd_zram_generator_unit_file_t, dir, "systemd-zram-setup@zram0.service.d")
      | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Error: Failed to parse files

[dburgener]

Merged, thanks!

It looks like we're coming up on a year since the last selint release, so I'll plan to do a release early in 2025 to get this and other recent fixes out.