skeema: Disable tests requiring network & fix deps
skeema: Disable tests requiring network & fix deps

- Disable the tests requiring access to gitlab.com.
- Add coreutils to `nativeBuildInputs` for printf and echo binaries.
- Fix hard coded paths to coreutils binaries.

Bug fixed by #173702 runs the previously skipped tests for this
package.

NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs