How to define category ID in an array?

As Geert pointed out, your current conditional will always be true.
An if() construct needs to be fed an expression.
You’re feeding it a valid array, so that’s true. Always.
So far this is basic PHP, regardless of whether in a WP environment or not.

As can be read in Chris_O’s comment

if ( is_category('some-cat') && is_tag('some-tag') ) {
    // do something
}

will do the trick.

'some-cat' and 'some-tag' may be the category/tag slug, id or title.
The codex page on conditional tags explains the use of these rather well.