tools: Fix error in is_tool_available.

- Happened with bandit, but not pycodestyle. Not sure why.

eris/eris/tools.py

@@ -657,7 +657,10 @@ def splitext(path):
 @functools.lru_cache()
 def is_tool_available(tool):
     if (hasattr(tool, "command") and tool.command.startswith(f"{PYTHON_EXECUTABLE} -m ")):
+        try:
             return importlib.util.find_spec(tool.command.split()[2]) is not None
+        except ModuleNotFoundError:
+            return False
     try:
         return all(shutil.which(executable) for executable in tool.executables)
     except AttributeError: