Hi, I need a little troubleshooting help. Every time I make changes to my home-manager configuration and `nixos-rebuild switch`, I get an error that `systemd-random-seed.service` failed to start. Restarting `home-manager-robin.service` on its own works fine, and this only happens when I change the home-manager config, not with the system. It looks like this is caused by the system units list being rebuilt? But I'm unable to find any mentions online of this issue, so I'm not exactly sure why.

```
› sudo nixos-rebuild switch
building Nix...
building the system configuration...
these derivations will be built:
  /nix/store/vzrqqhlb8lqjx2gpmi9mhfwjq2l35wi1-gammastep.service.drv
  /nix/store/vf9mffanl2ynqyi4p7c6grkcx38y4hxh-home-manager-files.drv
  /nix/store/ai45zf9q1bp6gv1b5mgcjwis28fr89ds-home-manager-generation.drv
  /nix/store/2qk7jhrr6j0f06fwja5qmfg2m0n3zyd7-activate-robin.drv
  /nix/store/1m1hsdnwh4psvrni792f0s6zcnm6c3w3-unit-home-manager-robin.service.drv
  /nix/store/mdmjsd7hw1r9x1r7i0352gjm1h5c8xsn-system-units.drv
  /nix/store/9kx65xgicwz1i9fqgbs4knsfk14ikp57-etc.drv
  /nix/store/jcchx472fg3ac6fxywx52981i03z610z-nixos-system-nuomoi-21.03pre261529.d9dba88d08a.drv
building '/nix/store/vzrqqhlb8lqjx2gpmi9mhfwjq2l35wi1-gammastep.service.drv'...
building '/nix/store/vf9mffanl2ynqyi4p7c6grkcx38y4hxh-home-manager-files.drv'...
building '/nix/store/ai45zf9q1bp6gv1b5mgcjwis28fr89ds-home-manager-generation.drv'...
building '/nix/store/2qk7jhrr6j0f06fwja5qmfg2m0n3zyd7-activate-robin.drv'...
building '/nix/store/1m1hsdnwh4psvrni792f0s6zcnm6c3w3-unit-home-manager-robin.service.drv'...
building '/nix/store/mdmjsd7hw1r9x1r7i0352gjm1h5c8xsn-system-units.drv'...
building '/nix/store/9kx65xgicwz1i9fqgbs4knsfk14ikp57-etc.drv'...
building '/nix/store/jcchx472fg3ac6fxywx52981i03z610z-nixos-system-nuomoi-21.03pre261529.d9dba88d08a.drv'...
stopping the following units: home-manager-robin.service
activating the configuration...
setting up /etc...
reloading user units for robin...
setting up tmpfiles
starting the following units: home-manager-robin.service
warning: the following units failed: systemd-random-seed.service

● systemd-random-seed.service - Load/Save Random Seed
     Loaded: loaded (/nix/store/4i7s80g57bqha7nna9yqcr50my0fva80-systemd-247.2/example/systemd/system/systemd-random-seed.service; enabled; vendor preset: enabled)
    Drop-In: /nix/store/qfblsxnicgcs9frsdxskynzrbb4kjyp0-system-units/systemd-random-seed.service.d
             └─overrides.conf
     Active: failed (Result: exit-code) since Sat 2021-01-09 20:41:37 EST; 395ms ago
       Docs: man:systemd-random-seed.service(8)
             man:random(4)
    Process: 7927 ExecStart=/nix/store/4i7s80g57bqha7nna9yqcr50my0fva80-systemd-247.2/lib/systemd/systemd-random-seed load (code=exited, status=1/FAILURE)
   Main PID: 7927 (code=exited, status=1/FAILURE)
         IP: 0B in, 0B out
        CPU: 3ms

Jan 09 20:41:37 nuomoi systemd[1]: Starting Load/Save Random Seed...
Jan 09 20:41:37 nuomoi systemd-random-seed[7927]: Failed to synchronize seed file: Input/output error
Jan 09 20:41:37 nuomoi systemd[1]: systemd-random-seed.service: Main process exited, code=exited, status=1/FAILURE
Jan 09 20:41:37 nuomoi systemd[1]: systemd-random-seed.service: Failed with result 'exit-code'.
Jan 09 20:41:37 nuomoi systemd[1]: Failed to start Load/Save Random Seed.
warning: error(s) occurred while switching to the new configuration
```