fix(db): use POSTGRES_HOST env var in dev Connect()

The dev-tagged Connect() in db_dev.go hardcoded localhost:5432 in the
DSN instead of reading the POSTGRES_HOST env var. Since CI tests run
with -tags "test,dev", db_dev.go is compiled and the POSTGRES_HOST=postgres
env var was silently ignored, causing db package tests to try connecting
to 127.0.0.1:5432 where no PostgreSQL is listening (service container
is only reachable via Docker DNS hostname postgres).

Also remove the -a flag from the workflow now that caching is no longer
suspected of causing issues.

.gitea/workflows/backend-tests.yaml

@@ -60,7 +60,7 @@ jobs:
 
       - name: Test (all packages)
         working-directory: backend
-        run: go test -a -tags "test,dev" -count=1 -v -timeout 120s ./handlers/... ./auth/... ./mw/... ./internal/... ./db/...
+        run: go test -tags "test,dev" -count=1 -v -timeout 120s ./handlers/... ./auth/... ./mw/... ./internal/... ./db/...
         env:
           POSTGRES_HOST: postgres
           PGUSER: myuser