Motivation for this change

This commit in the owslib repo added pyyaml as a dependency, so trying to build the derivation results in the following error message:

ERROR: Could not find a version that satisfies the requirement pyyaml (from OWSLib==0.19.2) (from versions: none)
ERROR: No matching distribution found for pyyaml (from OWSLib==0.19.2)

This commit adds pyyaml to the derivation as a runtime dep, so that it can build successfully.

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS linux)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Ensured that relevant documentation is up to date
• Fits CONTRIBUTING.md.