ci: fix saving build artifacts for osx and freebsd

When `${{ matrix.tarantool-branch}}` is `release/3.0` or similar, the
step to save build artifacts will fail with the following error:

    Error: Artifact name is not valid: osx-13-x86_64-release/3.0-debug.
    Contains the following character:  Forward slash /

This commit fixes the issue.

NO_DOC=ci
NO_TEST=ci
NO_CHANGELOG=ci