Fix wording in a release note; NFC

This change happened due to post-commit feedback on the review.

clang/docs/ReleaseNotes.rst

@@ -89,7 +89,7 @@ C++20 Feature Support
   an error to a warning under the ``-Wreserved-module-identifier`` warning
   group. This warning is enabled by default. This addresses `#61446
   <https://github.com/llvm/llvm-project/issues/61446>`_ and allows easier
-  building of precompiled modules. This diagnostic may be strengthened into an
+  building of standard modules. This diagnostic may be strengthened into an
   error again in the future once there is a less fragile way to mark a module
   as being part of the implementation rather than a user module.