Fix typo in docs "Migrate to JUnit 5 from JUnit 4"

[seraco]

What's changed?

Fixes a typo in the docs that caused the error:

Execution failed for task ':rewriteResolveDependencies'.
> Could not resolve all files for configuration ':detachedConfiguration1'.
   > Could not find org.openrewrite.recipe:rewrite-testing-frameworks:.
     Required by:
         project :

What's your motivation?

Prevent people from suffering the same error.

Checklist

• [ ] I've added unit tests to cover both positive and negative cases
• [ ] I've read and applied the recipe conventions and best practices
• [ ] I've used the IntelliJ IDEA auto-formatter on affected files

[timtebeek]

Thanks a lot for the fix @seraco ; I imagine this might affect a few of our other guides as well; would you mind double checking @mike-solomon ? Since you're about to change the version numbers here too

[mike-solomon]

I'll merge this in and take a look over the other docs and see. Thanks!