Fix snakemake rule existence checks

We use the existence of certain rules to control the DAG and the way
rules are stored internally changed in snakemake 7.32.1
<snakemake/snakemake@65c79a4>

This functionality is (probably?) only used for internal nextstrain builds
where we use the `auspice_config` rule to programmatically generate the
config.

workflow/snakemake_rules/main_workflow.smk

@@ -1394,6 +1394,15 @@ rule build_description:
         with open(output.description, "w", encoding = "utf-8") as o:
             o.write(template.safe_substitute(context))
 
+def rule_exists(name):
+    # Snakemake 7.32.1 changed the way rules are stored internally
+    # https://github.com/snakemake/snakemake/commit/65c79a48f956077839bb5ab1ea8d60a5f0ddecab
+    from packaging import version # an explicit dependency of augur
+    if version.parse(snakemake.__version__) < version.parse('7.32.1'):
+        return name in rules.__dict__
+    else:
+        return name in rules.__dict__['_rules']
+
 def get_auspice_config(w):
     """
     Auspice configs are chosen via this heirarchy:
@@ -1403,7 +1412,7 @@ def get_auspice_config(w):
     """
     if "auspice_config" in config["builds"].get(w.build_name, {}):
         return config["builds"][w.build_name]["auspice_config"]
-    if "auspice_config" in rules.__dict__:
+    if rule_exists("auspice_config"):
         return rules.auspice_config.output
     return config["files"]["auspice_config"]