Only test version of vim that work with ci

[idbrii]

Building with v8.0 fails with a warning explaining that this version of vim doesn't configure itself correctly:

Warning: This version of Vim has a bug where ./configure cannot find a
terminal library correctly. See the following issue for more details:
rhysd/action-setup-vim#38

Error: Command './configure --prefix=/Users/runner/vim-v8.0.0000 --with-features=huge --enable-fail-if-missing' exited non-zero status 1:
configure: error: NOT FOUND!
You need to install a terminal library; for example ncurses.
Or specify the name of the library with --with-tlib.

Use the version of vim that action-setup-vim identified as working. Also add v9 so we're still testing the same number of versions.

[idbrii]

Windows tests fail because they require sh:

  Before each
    let tempfile = s:tempfile()
    let config = Config.new_default_source()
    let config._values.browser_commands = [
    \ {'name': 'echo',
    \  'args': ['sh', '-c', 'echo "$1" > "$2"', '--', '{uri}', tempfile]}
    \]

The Windows-equivalent command would be cmd.exe, but it doesn't do that fancy argument substitution. I don't know vimscpec, but would something like this work?

    if has('win32')
      let config._values.browser_commands.args = ['cmd.exe', '/c', 'echo "{uri}" > ' .. tempfile]}
    endif