fix: Force renovate to keep alpine in docker version (attempt 2)

[lukemassa]

what

Second attempt at making renovate use the alpine version of the docker container for golang on upgrades.

why

First attempt (#5892) didn't work, trying again.

tests

This time I got some testing to work. I ran renovate locally and pulled out the relevant output.

On main:

             {
               "datasource": "docker",
               "depName": "golang",
               "displayPending": "`1.25.3`",
               "fixedVersion": "1.25.1-alpine",
               "currentVersion": "1.25.1-alpine",
               "currentValue": "1.25.1-alpine",
               "currentDigest": "sha256:b6ed3fd0452c0e9bcdef5597f29cc1418f61672e9d3a2f55bf02e7222c014abd",
               "newValue": "1.25.2",
               "newVersion": "1.25.2",
               "newDigest": "sha256:1c91b4f4391774a73d6489576878ad3ff3161ebc8c78466ec26e83474855bfcf",
               "packageFile": "Dockerfile",
               "updateType": "patch",
               "packageName": "golang"
             }

On the new branch

             {
               "datasource": "docker",
               "depName": "golang",
               "displayPending": "",
               "fixedVersion": "1.25.1-alpine",
               "currentVersion": "1.25.1",
               "currentValue": "1.25.1-alpine",
               "currentDigest": "sha256:b6ed3fd0452c0e9bcdef5597f29cc1418f61672e9d3a2f55bf02e7222c014abd",
               "newValue": "1.25.3-alpine",
               "newVersion": "1.25.3",
               "newDigest": "sha256:aee43c3ccbf24fdffb7295693b6e33b21e01baec1b2a55acc351fde345e9ec34",
               "packageFile": "Dockerfile",
               "updateType": "patch",
               "packageName": "golang"
             }

The last attempt #5886 attempted to put in this line

ARG GOLANG_TAG=1.25.2@sha256:1c91b4f4391774a73d6489576878ad3ff3161ebc8c78466ec26e83474855bfcf

I pulled the image locally and confirmed that was the hash. Both version name and hash match the renovate output on main above.

The new branch would imply a docker image golang:1.25.3-alpine with hash aee43c3ccbf24fdffb7295693b6e33b21e01baec1b2a55acc351fde345e9ec34, which I confirmed:

atlantis % docker pull golang:1.25.3-alpine
1.25.3-alpine: Pulling from library/golang
6b59a28fa201: Pull complete 
d32bb0dddca7: Pull complete 
5dab1238d3d9: Pull complete 
196fd7d83e7d: Pull complete 
4f4fb700ef54: Pull complete 
Digest: sha256:aee43c3ccbf24fdffb7295693b6e33b21e01baec1b2a55acc351fde345e9ec34

references

#5892