Add NodeJS version 21.x to test matrix

[ckairen]

No description provided.

[benbp]

Is the intent we add this for all tests or just a subset? If the former, there are a few more places these versions show up, see #27302

[ckairen]

Is the intent we add this for all tests or just a subset? If the former, there are a few more places these versions show up, see #27302

21 will soon be current in a couple of days, we'll probably want it in all tests? (we also did the same to node 17)

[mikeharder]

Is the intent we add this for all tests or just a subset? If the former, there are a few more places these versions show up, see #27302

21 will soon be current in a couple of days, we'll probably want it in all tests? (we also did the same to node 17)

Please try to see if any of the duplicate copies of node versions can be refactored to use a single copy we can update in one place.

[benbp]

@mikeharder I don't think there's much improvement here. The values are all set in different service directory custom matrix files. We'd have to introduce some sort of global variable for matrix pattern which I think is not worth it.