CI C tests fail

[JasonGross]

Since https://boringssl.googlesource.com/boringssl/+/aa31748bc84f0cd499e4b0337bf929b132aab1cc, our C tests fail with cp: cannot stat '/home/runner/work/fiat-crypto/fiat-crypto/fiat-c/src/curve25519_64_msvc.c': No such file or directory

Should we adjust

fiat-crypto/etc/ci/test-fiat-c-boringssl.sh

Line 29 in 457cb5e

( cd third_party/fiat && for i in *.h; do cp "${SUBCOMPONENT_PATH}/${i/.h/.c}" "$i" || exit $?; done ) || exit $?

to exclude these files?

Should we fix #1560?