[llvm][docs] Correct formatting in lldb release note

When you use <> in markdown it thinks it's an HTML tag
and does not show anything.

Author: DavidSpickett

llvm/docs/ReleaseNotes.md

@@ -311,7 +311,7 @@ Changes to LLDB
     stop reason = SIGSEGV: sent by tkill system call (sender pid=649752, uid=2667987)
   ```
 * ELF Cores can now have their siginfo structures inspected using `thread siginfo`.
-* Disassembly of unknown instructions now produces "<unknown>" instead of
+* Disassembly of unknown instructions now produces `<unknown>` instead of
   nothing at all
 * Changed the format of opcode bytes to match llvm-objdump when disassembling
   RISC-V code with `disassemble`'s `--byte` option.