Update "Unnamed Classes and Instance Main Methods (JEP 445)"

I would like to propose the following improvement on [this page](https://javaalmanac.io/features/jep445/):

* The feature was finalized in [JEP 456](https://openjdk.org/jeps/456)
* For consistency with the other feature articles  do not use a JEP number in the file name
* There is a typo in the JEP reference at the bottom: "JEP 445: ~String~ Unnamed Patterns and Variables (Preview), OpenJDK"