testsuite: Mark T11627b as fragile
testsuite: Mark T11627b as fragile

It was previously marked as broken due to #12236 however it passes for
me locally while failing on CI.

sdiehl/ghc,sdiehl/ghc,sdiehl/ghc,sdiehl/ghc,sdiehl/ghc,sdiehl/ghc,sdiehl/ghc