test: ignore the copied entry_point.c

Add `test_cannot_run_js/entry_point.c` to
`test/js-native-api/.gitignore`.

PR-URL: nodejs#48297
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: Gabriel Schulhof <gabrielschulhof@gmail.com>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
Reviewed-By: Darshan Sen <raisinten@gmail.com>
Reviewed-By: LiviaMedeiros <livia@cirno.name>
Reviewed-By: James M Snell <jasnell@gmail.com>

test/js-native-api/.gitignore

@@ -5,3 +5,4 @@ Makefile
 *.mk
 gyp-mac-tool
 /*/build
+test_cannot_run_js/entry_point.c