[ext-code-space][sandbox] Fix assert in BUILD.gn

Bug: v8:11985
Change-Id: I2d9cd602d9ef2491f0a757773bd4b110b03a064d
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3028381
Commit-Queue: Igor Sheludko <ishell@chromium.org>
Commit-Queue: Adam Klein <adamk@chromium.org>
Auto-Submit: Igor Sheludko <ishell@chromium.org>
Reviewed-by: Adam Klein <adamk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#75727}

BUILD.gn

@@ -480,7 +480,7 @@ assert(!v8_use_multi_snapshots || !v8_control_flow_integrity,
 assert(!v8_enable_heap_sandbox || v8_enable_pointer_compression,
        "V8 Heap Sandbox requires pointer compression")
 
-assert(!v8_enable_heap_sandbox || v8_enable_external_code_space,
+assert(!v8_enable_heap_sandbox || !v8_enable_external_code_space,
        "V8 Heap Sandbox is not compatible with external code space YET")
 
 assert(