dev: Temporarily pin ruamel.yaml <0.18.0 to work around Boa's issue

Boa uses a previously deprecated and now removed API in ruamel.yaml,
safe_load().  0.18.0 was the first version with its removal.

See <mamba-org/boa#376>.

Resolves <#44>.

devel/setup

@@ -39,6 +39,10 @@ create() {
 
         # Temporary pin until anaconda-client fixes dependency upstream
         "urllib3<2"
+
+        # Temporary pin until boa fixes dependency upstream
+        # <https://github.com/mamba-org/boa/issues/376>
+        "ruamel.yaml<0.18.0"
     )
 
     log "Creating new env with packages: ${pkgs[*]}"