chore: instructions on how to update Go (#4878)

---

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[Apache 2.0 license]: https://www.apache.org/licenses/LICENSE-2.0

Author: otaviomacedo

docs/updating-go-version.md

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+# Updating the Go version in jsii
+
+Each major Go release is supported until there are two newer major releases. When a Go release reaches it end of life,
+we should remove support for it in jsii. To do this, you have to:
+
+- Update the baseline version of Go in `.github/workflows/main.yml`.
+- Update `packages/@jsii/go-runtime/jsii-runtime-go/go.mod`
+- Update the value of the `GO_VERSION` constant in `packages/jsii-pacmak/lib/targets/go/package.ts`. Don't forget to
+  also update the `jsii-pacmak` jest snapshots.
+- Update `packages/@jsii/go-runtime-test/project/go.mod`.