Add riscv64 to GoReleaser build matrix and Docker images

[rajeshgangam]

Summary

• Add riscv64 to goarch in all goreleaser configs
• Add ignore rules for unsupported OS/arch combinations (darwin/riscv64, windows/riscv64, etc.)
• Add linux/riscv64 Docker platform builds and include riscv64 images in multi-arch Docker manifests

Go cross-compiles to linux/riscv64 natively with CGO_ENABLED=0, so no toolchain changes are needed.

Verified on native riscv64 hardware (BananaPi F3, SpacemiT K1) by @gounthar in #283 — gum, vhs, and glow all build and run without source changes.

Configs updated

Config	Binary	Docker
goreleaser-full.yaml	✅	✅
goreleaser.yaml	✅	✅
goreleaser-simple.yaml	✅	—
goreleaser-glow.yaml	✅	✅
goreleaser-semi.yaml	✅	✅
goreleaser-sequin.yaml	✅	—
goreleaser-soft-serve.yaml	✅	✅
goreleaser-vhs.yaml	✅	✅

Fixes #283

[gounthar]

Thanks for picking this up, @rajeshgangam.

One thing I noticed while reading through: in goreleaser-glow.yaml, goreleaser-semi.yaml, and goreleaser-soft-serve.yaml, the riscv64 dockers: build entry got added twice. The two blocks are identical, both producing ...:v{{ .Version }}-riscv64 on --platform=linux/riscv64. The other configs (goreleaser-full.yaml, goreleaser-vhs.yaml, goreleaser.yaml) only declare it once, which matches how amd64/arm64/armv7 are each declared a single time.

Removing the second riscv64 block in those three files should do it. Otherwise goreleaser ends up building and pushing the same tag twice during a release, and goreleaser check won't flag it since the schema is still valid.

The rest reads well to me: the per-file ignore rules line up with each config's goos list, and the manifest entries cover both docker.io and ghcr.io.

Once you've pushed a fix, I'm happy to test the resulting linux/riscv64 binaries and Docker images on a BananaPi F3. I have one here, so I can confirm gum/vhs/glow actually run.

[rajeshgangam]

Thanks for catching that! Removed the duplicate riscv64 Docker entries from all three files.