doc: clarify SEA platform support excludes darwin-x64

The Platform support section of the single-executable-applications doc
listed `macOS` without qualifying which architecture is supported.
SEA on x64 macOS is not supported and is skipped in CI; only arm64
macOS is exercised.

Refs: #62893
Signed-off-by: mokashang <64570909+mokashang@users.noreply.github.com>
PR-URL: #63181
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
Reviewed-By: Chemi Atlow <chemi@atlow.co.il>

Author: mokashang

doc/api/single-executable-applications.md

@@ -497,7 +497,8 @@ Single-executable support is tested regularly on CI only on the following
 platforms:
 
 * Windows
-* macOS
+* macOS (arm64 only; x64 is not currently supported and is skipped in the
+  tests)
 * Linux (all distributions [supported by Node.js][] except Alpine and all
   architectures [supported by Node.js][] except s390x)