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.

backend/db/db_dev.go

@@ -16,9 +16,10 @@ var Conn *PoolProxy
 func Connect() error {
 	// Connect to Postgres inside Docker network
 	dsn := fmt.Sprintf(
-		"postgres://%s:%s@localhost:5432/%s?sslmode=disable&require_auth=scram-sha-256",
+		"postgres://%s:%s@%s:5432/%s?sslmode=disable&require_auth=scram-sha-256",
 		getEnv("POSTGRES_USER"),
 		getEnv("POSTGRES_PASSWORD"),
+		getEnv("POSTGRES_HOST"),
 		getEnv("POSTGRES_DB"),
 	)