chore(tests): refactor assertions to use 'to.contain' instead of 'to.contains'

[kopernic-pl]

This pull request updates the test assertions across several command test suites to use the correct Chai assertion method. Specifically, it replaces .contains with .contain in all relevant expect statements, ensuring proper usage of the Chai library for string containment checks. No functional test logic or behavior is changed; these updates are solely to improve correctness and consistency in the test code.

Test assertion improvements:

• Replaced .contains with .contain in all expect statements in api/create.test.js to properly check error and output messages for various api:create scenarios. [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11]
• Updated .contains to .contain in api/delete.test.js for output validation when deleting API versions and definitions. [1] [2] [3] [4]
• Updated .contains to .contain in api/get.test.js for output validation in both JSON and YAML response formats. [1] [2] [3] [4] [5] [6] [7] [8]
• Updated .contains to .contain in api/publish.test.js, api/setdefault.test.js, and api/unpublish.test.js for publish, setdefault, and unpublish command output assertions. [1] [2] [3] [4]
• Updated .contains to .contain in api/update.test.js for both error and success output assertions in various api:update scenarios. [1] [2] [3] [4] [5] [6] [7] [8]