Add testrunner variant for --stress-concurrent-allocation

Bug: v8:10315
Change-Id: If64ff0bcd441ecce4113f70ba72373949f076efe
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2409276Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#69938}

tools/testrunner/local/variants.py

@@ -32,6 +32,7 @@ ALL_VARIANT_FLAGS = {
   "slow_path": [["--force-slow-path"]],
   "stress": [["--stress-opt", "--always-opt", "--no-liftoff",
               "--stress-lazy-source-positions"]],
+  "stress_concurrent_allocation": [["--stress-concurrent-allocation"]],
   "stress_js_bg_compile_wasm_code_gc": [["--stress-background-compile",
                                          "--stress-wasm-code-gc"]],
   "stress_incremental_marking": [["--stress-incremental-marking"]],