s/bookwork/bullseye to preserve glibc < 2.34 (#33546) (#33629)

With glibc 2.34 and the [removal of libpthread](https://developers.redhat.com/articles/2021/12/17/why-glibc-234-removed-libpthread), binaries built using [Debian bookworm](https://www.debian.org/releases/bookworm/) aren't compatible with older but still supported operating systems like RHEL8. In those environments, Mattermost fails to start with errors like:
```
mattermost/bin/mattermost: /lib64/libc.so.6: version `GLIBC_2.32' not found (required by mattermost/bin/mattermost)
mattermost/bin/mattermost: /lib64/libc.so.6: version `GLIBC_2.34' not found (required by mattermost/bin/mattermost)
```

One option might be to generate a static build and avoid the glibc dependency, but this kind of change is out of scope for now. Let's just revert back to using [Debian bullseye](https://www.debian.org/releases/bullseye/), which remains supported until at least August 2026.

(cherry picked from commit c2120b7224ce8d2f8dd34f17fbeba06296b733db)

Co-authored-by: Jesse Hallam <jesse.hallam@gmail.com>

server/.go-version

@@ -1 +1 @@
-1.24.3
+1.24.5

server/build/Dockerfile.buildenv

@@ -1,4 +1,4 @@
-FROM golang:1.24.3-bookworm@sha256:29d97266c1d341b7424e2f5085440b74654ae0b61ecdba206bc12d6264844e21
+FROM golang:1.24.5-bullseye@sha256:62ba6b19de03e891f7fa1001326bd48411f2626ff35e7ba5b9d890711ce581d9
 
 RUN apt-get update && apt-get install -y make git apt-transport-https ca-certificates curl software-properties-common build-essential zip xmlsec1 jq pgloader
 

server/go.mod

@@ -1,6 +1,6 @@
 module github.com/mattermost/mattermost/server/v8
 
-go 1.24.3
+go 1.24.5
 
 require (
 	code.sajari.com/docconv/v2 v2.0.0-pre.4

server/public/go.mod

@@ -1,6 +1,6 @@
 module github.com/mattermost/mattermost/server/public
 
-go 1.24.3
+go 1.24.5
 
 require (
 	github.com/blang/semver/v4 v4.0.0