Make android_compile_x64_rel actually compile in x64.

Due to a copy/paste error, the bot was compiling in x86.

Bug: webrtc:11097
Change-Id: I55b013f20707915886fa04956a37fb3fec0477b0
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/159931
Reviewed-by: Edward Lemur <ehmaldonado@webrtc.org>
Commit-Queue: Yves Gerey <yvesg@google.com>
Cr-Commit-Position: refs/heads/master@{#29825}

tools_webrtc/mb/mb_config.pyl

diff --git a/tools_webrtc/mb/mb_config.pyl b/tools_webrtc/mb/mb_config.pyl
index 480b608..fc87834 100644
--- a/tools_webrtc/mb/mb_config.pyl
+++ b/tools_webrtc/mb/mb_config.pyl
@@ -383,7 +383,7 @@
       'android', 'debug_static_bot', 'x64'
     ],
     'android_release_bot_x64': [
-      'android', 'release_bot', 'x86'
+      'android', 'release_bot', 'x64'
     ],
     'android_asan_shared_release_bot_arm': [
       'android', 'asan', 'clang', 'release_bot', 'arm'