www/shiori: Update to 1.6.0.r.4

• Use go 1.21 now
• Fix shiori version output:
  
  normal output:

Shiori version dev (build none) at unknown

patched output:

Shiori version 1.6.0-rc.4 (build FreeBSD) at 2023-11-09T08:25:04

Release notes: https://github.com/go-shiori/shiori/releases/tag/v1.6.0-rc.4
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