Avoid cloning kani submodules and fix enable-propproof flag

[zhassan-aws]

Description of changes:

As part of installing PropProof, the GitHub action currently clones the Kani repo (the proptest branch) and initializes its submodules recursively. This unnecessarily brings in submodules used for development, e.g. s2n-quic, nomicon, firecracker, etc. This PR removes the --recursive option to avoid bringing in those submodules.

This PR also fixes the enable-propproof input, which was always being evaluated to true, thus executing the PropProof step regardless of the input value.

Resolved issues:

Resolves #25

Related RFC:

Call-outs:

Testing:

• How is this change tested? Current tests

• Is this a refactor change? No

Checklist

• Each commit message has a non-empty body, explaining why the change was made
• Methods or procedures are documented
• Regression or unit tests are included, or existing tests cover the modified code
• My PR is restricted to a single feature or bugfix

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 and MIT licenses.

[zhassan-aws]

I'm actually now confused why the PropProof step runs in the first place in s2n-quic's CI given that it is guarded by the enable-propproof input, which is not used in s2n-quic's workflow. This is a bit orthogonal, but any ideas?

[zhassan-aws]

Filed this as #25

[zhassan-aws]

I added another commit (a6fd203) that fixes #25 as well.

[adpaco-aws]

Thanks @zhassan-aws for catching and fixing #25 !