[test] Mark pdfjs as slow for TSAN builds

Bug: v8:11600
Change-Id: I38696d64da4e321d966933179800376b7fdedaca
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3056987
Commit-Queue: Santiago Aboy Solanes <solanes@chromium.org>
Commit-Queue: Maya Lekova <mslekova@chromium.org>
Auto-Submit: Santiago Aboy Solanes <solanes@chromium.org>
Reviewed-by: Maya Lekova <mslekova@chromium.org>
Cr-Commit-Position: refs/heads/master@{#75961}

test/benchmarks/benchmarks.status

@@ -117,6 +117,7 @@
   'kraken/audio-dft': [SLOW],
   'kraken/audio-fft': [SLOW],
   'kraken/audio-oscillator': [SLOW],
+  'octane/pdfjs': [SLOW],
 }],  # 'tsan'
 
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