mulled-build-tool fix for packages wo version

for tools with requirements without version this resulted in a
conda install with requirement=None in the package specs
which does not work

lib/galaxy/tool_util/deps/mulled/mulled_build_tool.py

@@ -52,7 +52,7 @@ def requirements_to_mulled_targets(requirements) -> List["CondaTarget"]:
     Only package requirements are retained.
     """
     package_requirements = [r for r in requirements if r.type == "package"]
-    target_str = ",".join([f"{r.name}={r.version}" for r in package_requirements])
+    target_str = ",".join([f"{r.name}={r.version}" if r.version else r.name for r in package_requirements])
     targets = target_str_to_targets(target_str)
     return targets