ci: read the go version from go.mod in release.yml too

release.yml kept its own hardcoded go-version, so every tag push died at
`go mod download`:

  go: go.mod requires go >= 1.26.0 (running go 1.25.7; GOTOOLCHAIN=local)

The modules themselves published fine — the proxy serves them and consumers
resolve them — but the GitHub release job never ran. warden was unaffected
purely because its release.yml carried no pin at all.

This is the same stale pin in a third workflow location after the shared CI
call and the repo's own CI jobs. Every workflow now reads the directive from
go.mod via go-version-file, so there is no copy left to drift.

Author: juicycleff

.github/workflows/release.yml

@@ -43,7 +43,7 @@ jobs:
       - name: Set up Go
         uses: actions/setup-go@v6
         with:
-          go-version: "1.25.7"
+          go-version-file: go.mod
           cache: true
           cache-dependency-path: go.sum