Disable PopupPendingAndBackToSameSiteInstance on Site Isolation FYI bot.
Disable PopupPendingAndBackToSameSiteInstance on Site Isolation FYI bot.

RenderFrameHostManagerTest.PopupPendingAndBackToSameSiteInstance is
failing due to a recently discovered leak of RenderFrameImpls in
DiscardUnusedFrame in OOPIF-enabled modes.  This disables the test
on the FYI bots until the fix is landed.

TBR=jam
BUG=548275
TEST=Site Isolation FYI bots go green.

Review URL: https://codereview.chromium.org/1419593006

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#356493}

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