fix: custom directive doesn't work when custom=true

[decademoon]

Fix #2375.

[netlify]

✅ Deploy Preview for vue-router canceled.

Name	Link
🔨 Latest commit	0c6c6a0
🔍 Latest deploy log	https://app.netlify.com/sites/vue-router/deploys/6710828045c6dd000842d86f

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.39%. Comparing base (14219b0) to head (0c6c6a0).
Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2377   +/-   ##
=======================================
  Coverage   97.39%   97.39%           
=======================================
  Files          26       26           
  Lines        6032     6036    +4     
  Branches      824      826    +2     
=======================================
+ Hits         5875     5879    +4     
  Misses        155      155           
  Partials        2        2           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[posva]

Thanks!