fixed dynamically created properties

[opitz]

Dynamically created properties are deprecated.

[aydevworks]

doc blocks content not matching the properties names.

[aydevworks]

The phpunit test error could be fixed by the following code:

        // Get the academic year start date config (default is 08-01).
        $academicyearstartdate = get_config('block_lifecycle', 'academic_year_start_date') ?: '08-01';
        // Determine current academic year based on whether we've passed the start date.
        $currentyear = date('Y');
        $academicyearstart = strtotime($currentyear . '-' . $academicyearstartdate);
        if (time() < $academicyearstart) {
            // We haven't reached the academic year start date yet, so current academic year is last year.
            $currentacademicyear = $currentyear - 1;
        } else {
            $currentacademicyear = $currentyear;
        }

        // Put 4 years in associative array.
        $this->years = [
            'previous_year' => (string)($currentacademicyear - 2),
            'last_year' => (string)($currentacademicyear - 1),
            'current_year' => (string)$currentacademicyear,
            'next_year' => (string)($currentacademicyear + 1),
        ];

[andrewhancox]

Apologies - I didn't see this PR until I pushed mine up which (among other things) makes this change.