before-unload: the page is being left, not reloaded (cs, de)

[landsman]

The description of the before-unload plugin says the confirmation appears before the page is reloaded in German, which is narrower than what the code does: onbeforeunload fires whenever the page goes away — closing the tab, navigating elsewhere, or a reload.

• de: "bevor die Seite neu geladen wird" (before the page is reloaded) → "bevor die Seite verlassen wird".
• cs: "odnahráním" is not a word Czech uses for this; "opuštěním" is what the Croatian and Polish strings already say ("napuštanja", "rozładowaniem" → leaving).

The English doc-comment, hr and pl are correct and untouched. ja reads "before reloading the page" (再読込み) too, so it may want the same fix, but I do not speak Japanese well enough to propose the wording.

[landsman]

The red CI here is not from this change. PHPStan only analyses adminer/ and editor/ (conf/phpstan.neon), so plugins/before-unload.php is never looked at, and the same failure reproduces on an unmodified checkout of main at 29623c3:

Ignored error pattern booleanAnd.alwaysFalse was not matched in reported errors.

It arrived with PHPStan 2.2.6 (2.2.5 is green on the same tree) and php-actions/phpstan@v3 is pinned to version: latest.

#1310 fixes it in one line and its own run is green. Happy to rebase this branch once that lands so the check here goes green too.

[vrana]

Thanks and sorry about the CI error.