libcnb-test v0.4.0

• Leverage Into trait for String/&str arguments in ContainerContext (#412).
• Pass --trust-builder to pack build to ensure the builders used in tests are always trusted (#409).
• Add IntegrationTest::app_dir_preprocessor, allowing users to modify the app directory before an integration test run (#397).
• Update bollard dependency from 0.12.0 to 0.13.0 (#419).
• Update cargo_metadata dependency from 0.14.2 to 0.15.0 (#423).
• Add assert_not_contains! macro, an inverted version of assert_contains!. (#424).
• Remove IntegrationTest::run_test, to run a test use the new TestRunner::run_test function. (#422).
• Rename IntegrationTest to TestConfig. (#422).
• Rename IntegrationTestContext to TestContext. (#422).
• Add Clone implementation for TestConfig, allowing it to be shared across tests. (#422).
• Add TestContext::run_test, allowing you to run subsequent integration tests with the image from a previous test. These functions allow testing of subsequent builds, including caching logic and buildpack behaviour when build environment variables change, stacks are upgraded and more. (#422).
• Add TestConfig::expected_pack_result. When set to PackResult::Failure, it allows testing of build failure scenarios. (#429).
• Add TestConfig::app_dir which is handy in cases where TestConfig values are shared and only the app_dir needs to be different. (#430).
• Remove TestContext::app_dir to encourage the use of TestConfig::app_dir_preprocessor. (#431).
• Improve performance when no TestConfig::app_dir_preprocessor is configured by skipping application directory copying. (#431).