Mark source-frame-inline-breakpoint-decorations.js as flaky.

The test
http/tests/devtools/sources/debugger/source-frame-inline-breakpoint-decorations.js
has been flaking on the WebKit Linux MSAN builder for a while now, so
this CL marks it as flaky.

https://ci.chromium.org/p/chromium/builders/ci/WebKit%20Linux%20MSAN/7280

TBR=szuend@chromium.org

Bug: 1122742
Change-Id: Ifcb0ba10cbb792b04be4c922866a4f02dc54eb68
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2380436Reviewed-by: Scott Little <sclittle@chromium.org>
Commit-Queue: Scott Little <sclittle@chromium.org>
Cr-Commit-Position: refs/heads/master@{#802410}

third_party/blink/web_tests/TestExpectations

@@ -6641,3 +6641,4 @@ crbug.com/1120330 virtual/threaded/external/wpt/feature-policy/experimental-feat
 
 # Sheriff 2020-08-26
 crbug.com/1122106 external/wpt/webrtc/protocol/crypto-suite.https.html [ Pass Timeout ]
+crbug.com/1122742 http/tests/devtools/sources/debugger/source-frame-inline-breakpoint-decorations.js [ Pass Timeout ]