[CI] Unpin cargo-lambda version in `run-integration-test.yml`

[jlizen]

We had pinned back our cargo-lambda version due to CI failures. Ref: #989

The cargo-lambda issue was closed because it was determined that the issue had to do with the underlying zig install. essentially, you need libraries available, not just the binary. Ref: cargo-lambda/cargo-lambda#856 (comment)

This is the action that we use to install zig: https://github.com/marketplace/actions/setup-zig-compiler

I poked around a bit, and it does unpack the zig release tarball and seemingly adds the whole thing to path... so not sure exactly why it doesn't work. This needs more investigation.

Looks like there is a different issue actually, ref: mlugg/setup-zig#47 (comment)

Some unknown bug in cargo-zigbuild most likely.

[jlizen]

Cut a new issue in cargo-lambda since I can't re-open the existing one, and the issue is ongoing:
cargo-lambda/cargo-lambda#865