fix(deny): add a license field to irtt-integration-tests

cargo-deny's licenses check requires a license expression even on an
unpublished crate; add the workspace's Apache-2.0 license so the check
passes rather than treating irtt-integration-tests as unlicensed.

crates/irtt-integration-tests/Cargo.toml

@@ -2,6 +2,7 @@
 name = "irtt-integration-tests"
 version = "0.0.0"
 edition.workspace = true
+license.workspace = true
 rust-version.workspace = true
 publish = false