Query posts according to specific post meta values

Your syntax is complete wrong in your meta_query. A key/value pair in an array should be in the format of 'key' => 'value'. Your format is 'key', 'value' which in context of an array translate to 0 => 'key', 1 => 'value'. That is why your meta_query does not work.

Your failure is also due to not very good housekeeping. As your meta_query is written, it is hard to properly read it and because of that you miss obvious bugs.

Lets rewrite that section in a more readable way

$meta_query = [
    [
        'key'     => 'job_status',
        'value'   => 'open',
        'compare' => '!='
    ]
];
$query->set( 'meta_query', $meta_query );

As you can see, my code is easy to read, and very easy to spot obvious bug.

EDIT

If you need to add another key/value pair in your meta_query, you can simply just add another array.

$meta_query = [
    [
        'key'     => 'job_status',
        'value'   => 'open',
        'compare' => '!='
    ],
    [
        'key'     => 'another key',
        'value'   => 'another value',
        'compare' => '!='
    ]
];
$query->set( 'meta_query', $meta_query );