strict (not-)equal checks

[ximex]

use strict (not-)equal checks in db/, src/, tests/
unit tests still works

[MyIgel]

To be honest i don't see a good reason her (besides having to type more characters and remember to do so). SO we are here at a discussion of basics which should literally be an issue instead of a PR

[ximex]

sorry but typing one more char is no real argument for me to reject this change. the remembering argument is solved by the phpcs rule.
Using only == or != instead of === or !== could lead to problems if you compare things like 1 with '1' or want to differentiate '' and null and []. In every software project i worked with everyone also thought so that this is a good change.
see: https://www.php.net/manual/en/types.comparisons.php