Merge: #21079: is_attachment now looks only at the value, ignoring parameters.

diff --cc Misc/NEWS
index 1a02975986d1bf139da03705f492feb391dfc829,c5afa50c83722a891612c4f013a9cbb3c88334d3..e4edc4cf39e8e09566862d4e81e755fbd14d5161
--- 1/Misc/NEWS
--- 2/Misc/NEWS
+++ b/Misc/NEWS
@@@ -137,12 -32,11 +137,15 @@@ Core and Builtin
  Library
  -------
  
+ - Issue #21079: Fix email.message.EmailMessage.is_attachment to return the
+   correct result when the header has parameters as well as a value.
+ 
  - Issue #22247: Add NNTPError to nntplib.__all__.
  
 +- Issue #22366: urllib.request.urlopen will accept a context object
 +  (SSLContext) as an argument which will then used be for HTTPS connection.
 +  Patch by Alex Gaynor.
 +
  - Issue #4180: The warnings registries are now reset when the filters
    are modified.