Support @testing-library/react v13.x

[apaatsio]

slate-test-utils@1.3.2 depends on @testing-library/react v12. Trying to install slate-test-utils with @testing-library/react v13 fails.

$ npm i --save-dev slate-test-utils                                                                                                                     
npm ERR! code ERESOLVE
npm ERR! ERESOLVE unable to resolve dependency tree
npm ERR! 
npm ERR! While resolving: my-project@0.1.0
npm ERR! Found: @testing-library/react@13.3.0
npm ERR! node_modules/@testing-library/react
npm ERR!   dev @testing-library/react@"13.3.0" from the root project
npm ERR! 
npm ERR! Could not resolve dependency:
npm ERR! peer @testing-library/react@"^12.1.2" from slate-test-utils@1.3.2
npm ERR! node_modules/slate-test-utils
npm ERR!   dev slate-test-utils@"*" from the root project
npm ERR! 
npm ERR! Fix the upstream dependency conflict, or retry
npm ERR! this command with --force, or --legacy-peer-deps
npm ERR! to accept an incorrect (and potentially broken) dependency resolution.

• slate-test-utils: 1.3.2
• testing-library/react: 13.3.0
• node: 14.18.2
• npm: 7.24.2