Passkey importer: fix file picker parent

When selecting "Database → Import Passkey", we show a file picker.
Previously, we did not specify a parent widget for it. This could have
undesirable effects on its presentation. (For example, with the Sway
tiling Wayland compositor, it would show the file picker as a tiled
window rather than a floating one.)

Fix the issue by passing in the parent widget. This is also in line with
all other usages of FileDialog::getOpenFileName() in this project.

src/gui/passkeys/PasskeyImporter.cpp

@@ -39,7 +39,7 @@ void PasskeyImporter::importPasskey(QSharedPointer<Database>& database, Entry* e
 {
     auto filter = QString("%1 (*.passkey);;%2 (*)").arg(tr("Passkey file"), tr("All files"));
     auto fileName =
-        fileDialog()->getOpenFileName(nullptr, tr("Open passkey file"), FileDialog::getLastDir("passkey"), filter);
+        fileDialog()->getOpenFileName(m_parent, tr("Open passkey file"), FileDialog::getLastDir("passkey"), filter);
     if (fileName.isEmpty()) {
         return;
     }