[Sheriff] Mark fast/dom/cssTarget-crash.html flaky with timeout

Seems to be timing out again on Linux debug, but not on other platforms.

See:
https://ci.chromium.org/p/chromium/builders/ci/Linux%20Tests%20%28dbg%29%281%29/93029

TBR=masonfreed@chromium.org

Bug: 1095379, 1105957
Change-Id: Ie8ee802ce51a20ba52edbc961a38b5a023bf6cbb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2545508Reviewed-by: Ioana Pandele <ioanap@chromium.org>
Commit-Queue: Ioana Pandele <ioanap@chromium.org>
Cr-Commit-Position: refs/heads/master@{#828724}

third_party/blink/web_tests/TestExpectations

@@ -6015,3 +6015,4 @@ crbug.com/1146221 [ Linux ] http/tests/devtools/sources/debugger-ui/debugger-inl
 
 # Sheriff 2020-11-18
 crbug.com/915903 http/tests/security/inactive-document-with-empty-security-origin.html [ Pass Timeout ]
+crbug.com/1105957 [ Linux Debug ] fast/dom/cssTarget-crash.html [ Pass Timeout ]