Hi,

Whilst working on the Reproducible Builds effort [0], we noticed that
rust-opam-file-rs could not be built reproducibly.

This is because running the testsuite generates a parser.rs file which
gets included in the binary package. This means that if the tests are
skipped, then the package will not include this file... meaning that the
package is unreproducible.

Patch attached.

 [0] https://reproducible-builds.org/


Regards,