Ratchet tests use some invalid private keys

[mmdriley]

Two of the private keys in test_ratchet.c (here and here) aren't valid Curve25519 keys. Their first bytes aren't divisible by 8.

I noticed this by uncommenting these lines in curve25519-donna.c, which should be redundant for valid secret keys. Instead, uncommenting those lines causes the tests to fail because the computed agreements change.

[dkonigsberg]

Unfortunately these key bytes come directly from the equivalent unit tests in libsignal-protocol-java (here and here)

Since the unit tests in the C version are intended to be duplicates of the Java version's test cases whenever possible, they will not be changed unless equivalent changes are made to the Java version's unit tests.

As such, please report this issue on the Java version's project page.