Bump Go version from 1.23.1 to 1.23.4, Alpine on Docker images from 3.20 to 3.21 (#24518)

Kept the Debian-based image at Bullseye.

For #24517.

# Checklist for submitter

- [x] Changes file added for user-visible changes in `changes/`,
`orbit/changes/` or `ee/fleetd-chrome/changes`.
See [Changes
files](https://github.com/fleetdm/fleet/blob/main/docs/Contributing/Committing-Changes.md#changes-files)
for more information.
- [x] Manual QA for all new/changed functionality: Validated builds
(Docker and make) all work after this change, except for BitLocker
(requires Windows).

infrastructure/loadtesting/terraform/docker/loadtest.Dockerfile

@@ -1,9 +1,9 @@
-FROM golang:1.23.1-alpine3.20@sha256:436e2d978524b15498b98faa367553ba6c3655671226f500c72ceb7afb2ef0b1
+FROM golang:1.23.4-alpine3.21@sha256:052793ea3143a235a5b2d815ccead8910cfe547b36a1f4c8b070015b89da5eab
 ARG TAG
 RUN apk add git
 RUN git clone -b $TAG --depth=1 --no-tags --progress --no-recurse-submodules https://github.com/fleetdm/fleet.git && cd /go/fleet/cmd/osquery-perf/ && go build .
 
-FROM alpine:3.20@sha256:77726ef6b57ddf65bb551896826ec38bc3e53f75cdde31354fbffb4f25238ebd
+FROM alpine:3.21@sha256:2c43f33bd1502ec7818bce9eea60e062d04eeadc4aa31cad9dabecb1e48b647b
 LABEL maintainer="Fleet Developers"
 
 # Create FleetDM group and user