ci: update Nix installation and caching

- Added the flag "--accept-flake-config" to the "nix develop" command in the CI workflow file.
- This flag allows the development profile to be built using the dev-profiile flake configuration.
- The purpose of this change is to ensure that the CI workflow can successfully build and test the project.

.github/workflows/ci.yml

@@ -47,5 +47,5 @@ jobs:
         with:
           name: peerswap
           authToken: '${{ secrets.CACHIX_AUTH_TOKEN }}'
-      - run: nix develop --profile dev-profiile
+      - run: nix develop --profile dev-profiile --accept-flake-config
       - run: "make test-${{matrix.test-vector}}"