build: set min build version to Go 1.22.6

Go 1.23 was released this week, so with this PR we update the build
system to officially support the last two releases.

lnrpc/gen_protos_docker.sh

@@ -6,7 +6,7 @@ set -e
 DIR="$(cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd)"
 
 # golang docker image version used in this script.
-GO_IMAGE=docker.io/library/golang:1.21.4-alpine
+GO_IMAGE=docker.io/library/golang:1.22.6-alpine
 
 PROTOBUF_VERSION=$(docker run --rm -v $DIR/../:/lnd -w /lnd $GO_IMAGE \
   go list -f '{{.Version}}' -m google.golang.org/protobuf)