Append "_latest" to image id if no tag is present (#2085)

Author: sameeul

cwltool/singularity.py

@@ -134,10 +134,14 @@ def is_version_3_10_or_newer() -> bool:
 
 
 def _normalize_image_id(string: str) -> str:
+    if ":" not in string:
+        string += "_latest"
     return string.replace("/", "_") + ".img"
 
 
 def _normalize_sif_id(string: str) -> str:
+    if ":" not in string:
+        string += "_latest"
     return string.replace("/", "_") + ".sif"