CI: use npx to call the binary

[dylanirlbeck]

Can you give some more context on why this change is needed?

[tatchi]

I have been testing the ppx on a windows machine and got an error. I was surprised that it was not caught by the CI. I actually found out that we were not calling the binary correctly (we need to use npx). That's why it was printing nothing on Windows previously:

The error was reported in https://github.com/esy/esy/issues/1160#issue-688022785 and using esy 0.6.4 fixes it.

• First commit use npx to call the binary -> you can see the error on windows
• Second commit switch to esy@0.6.4 -> no more error and the result of the binary is correctly printed

[ManasJayanth]

@dylanirlbeck Following up from the issue at esy/esy#1160 , what happened was esy incorrectly assumed rewritePrefix is true. Explicitly setting rewritePrefix to true in the esy.json can avoid this problem and still continue the use of 0.6.6.

To give some more context: rewritePrefix is alpha quality feature. It was earlier made opt-in in the earliers releases, but recently the rewriting behaviour has seen improvements. It would really help if more users opt into using it and providing feedback.

[dylanirlbeck]

@ManasJayanth Awesome, thanks for the explanation.