[debuginfo-test][cross-project-tests] Release note for new project name

Add a release note for the renaming of the debuginfo-test to
cross-project-tests, performed in commit
1364750d and follow-ons.

Reviewed by: sylvestre.ledru

Differential Revision: https://reviews.llvm.org/D110134

llvm/docs/ReleaseNotes.rst

@@ -57,6 +57,15 @@ Non-comprehensive list of changes in this release
 
 * Flang is now included in the binary packages released by LLVM.
 
+* The debuginfo-test project has been renamed cross-project-tests and is now
+  intended for testing components from multiple projects, not just debug
+  information. The new "cross-project-tests" name replaces "debuginfo-test" in
+  LLVM_ENABLE_PROJECTS, and a new check-cross-project-tests target has been
+  added for running all tests in the project. The pre-existing check-debuginfo-
+  test target remains for running just the debug information tests.
+  (`D95339 <https://reviews.llvm.org/D95339>`_ and
+  `D96513 <https://reviews.llvm.org/D96513>`_)
+
 Changes to the LLVM IR
 ----------------------