landlock: Improve erratum documentation

Improve description about scoped signal handling.

Reported-by: Günther Noack <gnoack3000@gmail.com>
Link: https://lore.kernel.org/r/20251219193855.825889-2-mic@digikod.net
Reviewed-by: Günther Noack <gnoack3000@gmail.com>
Signed-off-by: Mickaël Salaün <mic@digikod.net>

Author: l0kod

security/landlock/errata/abi-6.h

@@ -9,7 +9,7 @@
  * This fix addresses an issue where signal scoping was overly restrictive,
  * preventing sandboxed threads from signaling other threads within the same
  * process if they belonged to different domains.  Because threads are not
- * security boundaries, user space might assume that any thread within the same
+ * security boundaries, user space might assume that all threads within the same
  * process can send signals between themselves (see :manpage:`nptl(7)` and
  * :manpage:`libpsx(3)`).  Consistent with :manpage:`ptrace(2)` behavior, direct
  * interaction between threads of the same process should always be allowed.