fix: set GOPRIVATE in release workflow to fix module resolution

Go proxy cannot resolve github.com/openprx/fenfa as it's a new repo.
Set GOPRIVATE to skip proxy/checksum for our own module.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: g1e2x87

.github/workflows/release.yml

@@ -8,6 +8,9 @@ on:
 permissions:
   contents: write
 
+env:
+  GOPRIVATE: github.com/openprx/*
+
 jobs:
   build:
     runs-on: ubuntu-latest