Bug 1642732 [wpt PR 23917] - Update interfaces/fetch.idl, a=testonly

Automatic update from web-platform-tests
Update interfaces/fetch.idl (#23917)

Source: https://github.com/tidoust/reffy-reports/blob/e5e4f6a/ed/idl/fetch.idl
Build: https://travis-ci.org/tidoust/reffy-reports/builds/693970304
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wpt-commits: 41f4fd6d3d89525170809a029c2c00e3d926e666
wpt-pr: 23917

Differential Revision: https://phabricator.services.mozilla.com/D78792

Author: autofoolip

testing/web-platform/tests/interfaces/fetch.idl

@@ -17,7 +17,9 @@ interface Headers {
   iterable<ByteString, ByteString>;
 };
 
-typedef (Blob or BufferSource or FormData or URLSearchParams or ReadableStream or USVString) BodyInit;
+typedef (Blob or BufferSource or FormData or URLSearchParams or USVString) XMLHttpRequestBodyInit;
+
+typedef (ReadableStream or XMLHttpRequestBodyInit) BodyInit;
 interface mixin Body {
   readonly attribute ReadableStream? body;
   readonly attribute boolean bodyUsed;