docker: Update image to golang:1.19.1-alpine3.16.

This updates the docker image to golang:1.19.1-alpine3.16.

To confirm the new digest:

```
$ docker pull golang:1.19.1-alpine3.16
...
1.19.1-alpine3.16: Pulling from library/golang
...
Digest: sha256:d475cef843a02575ebdcb1416d98cd76bab90a5ae8bc2cd15f357fc08b6a329f
...
```

contrib/docker/Dockerfile

@@ -7,13 +7,13 @@
 ###############
 
 # Basic Go environment with git, SSL CA certs, and upx.
-# The image below is golang:1.19.0-alpine3.16 (linux/amd64)
+# The image below is golang:1.19.1-alpine3.16 (linux/amd64)
 # It's pulled by the digest (immutable id) to avoid supply-chain attacks.
 # Maintainer Note:
 #    To update to a new digest, you must first manually pull the new image:
 #    `docker pull golang:<new version>`
 #    Docker will print the digest of the new image after the pull has finished.
-FROM golang@sha256:0e78fc17d9b4428bc6b9c07aa49c819541a99cd0c0121c4de9c68feecfea825b AS builder
+FROM golang@sha256:d475cef843a02575ebdcb1416d98cd76bab90a5ae8bc2cd15f357fc08b6a329f AS builder
 RUN apk add --no-cache git ca-certificates upx
 
 # Empty directory to be copied into place in the production image since it will