deps(docker): bump golang in /docker/tools

Bumps golang from 1.21-bullseye to 1.22-bullseye.

---
updated-dependencies:
- dependency-name: golang
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

docker/tools/Dockerfile

@@ -1,5 +1,5 @@
 # Build Kopia binary
-FROM golang:1.21-bullseye AS builder
+FROM golang:1.22-bullseye AS builder
 
 ARG kopia_build_commit=master
 ARG kopia_repo_org=kopia