re-activate abc warnings

Author: fchapoton

src/sage/all.py

@@ -94,10 +94,6 @@
 warnings.filterwarnings('ignore', category=DeprecationWarning,
     module='(scipy|networkx)')
 
-# Ignore collections.abc warnings, there are a lot of them but they are
-# harmless.
-warnings.filterwarnings('ignore', category=DeprecationWarning,
-    message='.*collections[.]abc.*')
 # However, be sure to keep OUR deprecation warnings
 warnings.filterwarnings('default', category=DeprecationWarning,
     message=r'[\s\S]*See https?://trac\.sagemath\.org/[0-9]* for details.')
@@ -323,6 +319,7 @@ def quit_sage(verbose=True):
 # From now on it is ok to resolve lazy imports
 sage.misc.lazy_import.finish_startup()
 
+
 def sage_globals():
     r"""
     Return the Sage namespace.