[fastcall] Fix the syntax of stress_snapshot entry

This CL fixes the syntax of an entry in variants.py for stress_snapshot
(which got introduced in
https://chromium-review.googlesource.com/c/v8/v8/+/3024147).

Change-Id: I8e25ce26d546a022dbf9c038719f3e7cfac1d250
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3031898
Auto-Submit: Maya Lekova <mslekova@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#75748}

tools/testrunner/local/variants.py

@@ -62,7 +62,7 @@ INCOMPATIBLE_FLAGS_PER_VARIANT = {
   # serialized to the snapshot, so we don't have a
   # SerializeInternalFieldsCallback for it, so they are incompatible with
   # stress_snapshot.
-  "stress_snapshot": [["--turbo-fast-api-calls"]],
+  "stress_snapshot": ["--turbo-fast-api-calls"],
   "stress": ["--always-opt", "--no-always-opt",
              "--max-inlined-bytecode-size=*",
              "--max-inlined-bytecode-size-cumulative=*", "--stress-inline",