Fix two more flaky tests (#11095)

* mode_spec: retry with increasing matchtime

`matchtime=2` might still be too low (with luacov on AppVeyor).

    [  ERROR   ] test/functional\ui\mode_spec.lua @ 47: ui mode_change event works in insert mode
    test\functional\ui\screen.lua:587: mode
    Expected objects to be the same.
    Passed in:
    (string) 'insert'
    Expected:
    (string) 'showmatch'
    Hint: full state of "mode":
      "insert"

Followup to fe60013fb.
ref #10941
Initially regressed in 7ed2122622

``

* ui/screen_basic_spec: set timeoutlen=10000

This fixes the test on slow CI.

Ref: https://ci.appveyor.com/project/neovim/neovim/builds/27600387/job/t468h2b3w9lwtlm5#L10930

test/functional/ui/screen_basic_spec.lua

@@ -915,6 +915,7 @@ local function screen_tests(linegrid)
 
   -- Regression test for #8357
   it('does not have artifacts after temporary chars in insert mode', function()
+    command('set timeoutlen=10000')
     command('inoremap jk <esc>')
     feed('ifooj')
     screen:expect([[