use custom ci image

.github/workflows/verify.yml

@@ -9,7 +9,7 @@ on:
 jobs:
   verify:
     runs-on: ubuntu-latest
-    container: gcc:15
+    container: sfja/h5-mst-ci-backend
 
     steps:
     - uses: actions/checkout@v4

backend/ci-container/Dockerfile

@@ -0,0 +1,3 @@
+FROM alpine:3.14
+RUN apk add gcc llvm
+

backend/ci-container/publish.sh

@@ -0,0 +1,10 @@
+#!/bin/bash
+
+tag=sfja/h5-mst-ci-backend
+
+set -xe
+
+docker build -t $tag .
+
+docker push $tag
+