bug#32764: Somne flymake tests seem unstable

[Glenn Morris]

Package: emacs
Version: 27.0.50
Severity: minor

Ref: https://hydra.nixos.org/build/81615914

I've seen some flymake test failures like the following a few times.
Perhaps some timeout needs to be increased.

    Test included-c-header-files condition:
        (ert-test-failed "Some backends not reporting yet (flymake-cc)")
       FAILED  4/9  included-c-header-files (10.545006 sec)

    Test perl-backend condition:
        (error "Selecting deleted buffer")
       FAILED  5/9  perl-backend (0.289559 sec)

    Test recurrent-backend condition:
        (error "Selecting deleted buffer")
       FAILED  6/9  recurrent-backend (0.005780 sec)

    Test warning-predicate-function-gcc condition:
        (ert-test-failed "Some backends not reporting yet (flymake-cc)")
       FAILED  8/9  warning-predicate-function-gcc (5.444343 sec)