Do not try to fetch last modified date if remote file (#707)

If the file given in the artifact is not local, then the code should not
attempt to fetch the last modified date.

This applies to cases where the file is "-" meaning standard input and
artifacts with a URL when targeting GitHub repos and such.

Signed-off-by: Eric Brown <eric.brown@securesauce.dev>

precli/core/artifact.py

@@ -15,7 +15,7 @@ def __init__(self, file_name: str, uri: Optional[str] = None):
         self._encoding = "utf-8"
         self._language = None
 
-        if file_name != "-" or not uri:
+        if file_name != "-" and not uri:
             modified_time = os.path.getmtime(file_name)
             self._last_modified = datetime.fromtimestamp(
                 modified_time, tz=timezone.utc