Don't check directory atime in lstat_stat_variation10.phpt test

This is a funny one. I discovered that lstat_stat_variation10.phpt was failing every
now and again when the PHP test suite was run on my dev PC. The output from the failing
test showed that the atime (access time) of the directory created in the test was changing
between these lines:

    $old_stat = stat($dirname);
    clearstatcache();
    sleep(1);
    var_dump( is_dir($dirname) );
    $new_stat = stat($dirname);

Could is_dir() be accessing the directory and changing the atime? strace showed that is_dir
was only issuing a single stat() syscall. Could stat() change the atime? No, no, that would
just be perverse. Nobody would be stupid enough to implement the kernel in that way.

Checked the kernel source, found that the function called when atime needs to be updated
appears to be touch_atime(). Broke out the BCC kernel tracing tools and ran this one
while running the flaky test case in a loop:

    sudo trace -I<kernel src dir>/include/linux/path.h -I<same>/include/linux/dcache.h 'touch_atime(struct path *path) "%s", path->dentry->d_name.name'

Inspecting the results showed that something called "git_thread" was occcasionally updating
the atime on the directory in question!! What on earth...???

The PID shown by trace revealed that this was a background thread for Sublime Text 3.
Sublime now has git integration and shows when there are untracked or modified files. It
seems that it uses a background thread to regularly scan the project directory and look
for new and modified files. This was causing the atime to change.

Even though other developers may not be running ST3, there are any number of reasons why
a background process might recurse through various directories and could cause the atime
to change unexpectedly. Therefore, update the test case so it doesn't fail in such cases.

Closes GH-5553.

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