ci(tenant-registry): downgrade go directive 1.25 → 1.24

The runner's golangci-lint binary is built with Go 1.24 and refuses
to lint modules targeting a higher Go version ('the Go language
version (go1.24) used to build golangci-lint is lower than the
targeted Go version (1.25)'). 1.24 is current stable and covers
everything the skeleton uses (slog, ServeMux method routing).

Dockerfile pinned to golang:1.24-alpine to match.

Refs: M4.1

Dockerfile

@@ -1,6 +1,6 @@
 # Multi-stage build for tenant-registry.
 
-FROM golang:1.25-alpine AS build
+FROM golang:1.24-alpine AS build
 WORKDIR /src
 COPY go.mod ./
 RUN go mod download

go.mod

@@ -1,3 +1,3 @@
 module gitea.meghsakha.com/platform/tenant-registry
 
-go 1.25
+go 1.24