Bump library/golang from 1.22.3 to 1.22.4 in /testserver

Bumps library/golang from 1.22.3 to 1.22.4.

---
updated-dependencies:
- dependency-name: library/golang
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

testserver/Dockerfile

@@ -1,4 +1,4 @@
-FROM docker.io/library/golang:1.22.3 AS builder
+FROM docker.io/library/golang:1.22.4 AS builder
 WORKDIR /go/src/github.com/airtower-luna/referer-mod/testserver/
 COPY go.mod server.go ./
 RUN CGO_ENABLED=0 go build