chore(schema-engine): silence the unused-variable warning in a flavourless build
Every arm of the connection string comparison is behind a flavour feature, so a
build with none of them enabled has nothing left to compare and no use for the
arguments. That build is what `cargo check -p schema-engine-wasm` does by default.
Signed-off-by: Alexey Orlenko's AI Agent <robot@aqrln.net>