Allow true return annotation in upgrade.php function

[daniil-berg]

Technically, the xmldb_..._upgrade function in db/upgrade.php always returns true. Since PHP 8.2 you can actually annotate it accordingly. I discovered that doing so causes this weird warning from the savepoints checker:

    + WARN: Detected fewer 'if' blocks (0) than 'savepoint' calls (1). Repeated savepoints?
    + NOTE: cannot find 'if' blocks within the upgrade function

This PR just extends the function RegEx to also match a true return type annotation, not just one with bool. (Also being more lenient with the whitespace here would not hurt since this is not a style checker.)

It seems tests/check_upgrade_savepoints.bats does the testing and there already is the tests/fixtures/check_upgrade_savepoints/returning_bool.patch fixture for bool return types. But I have never seen this type of testing setup before, so I am not sure how best to add a corresponding test case.

If you tell me how I should go about it, I am sure adding a test case for this should not be too difficult.