Switch libfuzzer_msan_release_bot to release builds.

This is a speculative CL to temporarily workaround the issue reported
on crbug.com/1025796. It seems that starting from [1] the bot started to
report errors like:

>>> referenced by string_traits_wtf.cc
>>>               obj/mojo/public/cpp/bindings/wtf_support/string_traits_wtf.o:(sancov.module_ctor_8bit_counters)

And they look quite similar to what was reported on crbug.com/912919
(which was blocked on the WebRTC component build support) and it that
case the solution has been to temporarily switch back to release builds
(see https://chromium-review.googlesource.com/c/chromium/src/+/1367652).

[1] - https://chromium-review.googlesource.com/c/chromium/src/+/1874722

TBR: ehmaldonado@chromium.org
Bug: 1025796
Change-Id: Ic5261df5cd4569fb5b76ffc7d82e8aacc9d9191b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1920824
Commit-Queue: Mirko Bonadei <mbonadei@chromium.org>
Reviewed-by: Max Moroz <mmoroz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#716327}

tools/mb/mb_config.pyl

@@ -1805,7 +1805,7 @@
     ],
 
     'libfuzzer_msan_release_bot': [
-      'libfuzzer', 'msan', 'shared_release_bot', 'chromeos_codecs', 'pdf_xfa', 'disable_nacl', 'optimize_for_fuzzing', 'disable_seed_corpus',
+      'libfuzzer', 'msan', 'release_bot', 'chromeos_codecs', 'pdf_xfa', 'disable_nacl', 'optimize_for_fuzzing', 'disable_seed_corpus',
     ],
 
     'libfuzzer_ubsan_release_bot': [