[NFC] Fix formatting for release notes

This was causing a build failure due to using the incorrect syntax
for quoting.

Author: Stylie777

llvm/docs/ReleaseNotes.rst

@@ -76,10 +76,10 @@ Changes to the AArch64 Backend
 * Added support for Cortex-A78AE, Cortex-A520AE, Cortex-A720AE,
   Cortex-R82AE, Neoverse-N3, Neoverse-V3 and Neoverse-V3AE CPUs.
 
-* `-mbranch-protection=standard` now enables FEAT_PAuth_LR by
+* ``-mbranch-protection=standard`` now enables FEAT_PAuth_LR by
   default when the feature is enabled. The new behaviour results 
-  in `standard` being equal to `bti+pac-ret+pc` when `+pauth-lr` 
-  is passed as part of `-mcpu=`options. 
+  in ``standard`` being equal to ``bti+pac-ret+pc`` when ``+pauth-lr``
+  is passed as part of ``-mcpu=`` options.
 
 Changes to the AMDGPU Backend
 -----------------------------