Attempt to fix and debug read-only filesystem issue at build.

.gitea/workflows/test.yaml

@@ -9,3 +9,4 @@ jobs:
     steps:
       - uses: actions/checkout@v4
       - run: scripts/run-end-to-end-tests
+      - run: find . -name borgmatic-1.8.9.dev0

tests/end-to-end/docker-compose.yaml

@@ -49,7 +49,8 @@ services:
     environment:
       TEST_CONTAINER: true
     volumes:
-      - "../..:/app:ro"
+#      - "../..:/app:ro"
+      - "../..:/app"
     tmpfs:
       - "/app/borgmatic.egg-info"
       - "/app/build"