ci: change to sha hashes

[JSeam2]

Changes:

1. Changes all the imports in github actions to use SHA hashes instead for reproducibility and supply chain safety.

Notes:
It is necessary to manually update the nightly commit hash in .github/workflows/release.yml in the following section should this PR be merged

      - name: Install Rust
        uses: dtolnay/rust-toolchain@4f94fbe7e03939b0e674bcc9ca609a16088f63ff  #nightly branch, TODO: update when required
        with:
          target: ${{ matrix.target }}

2. Fixes the ezkl-gpu sed commands