fix: No password set for new mail shares

Before the password is set on a new share, the computed property `hasUnsavedPassword`
is used to check that `this.share.newPassword` is not undefined. Direct assignment without
using Vue's `this.$set` makes it impossible for vue to detect that changes have happened on the share
object. Hence the inreactivity.

This worked initially most likely because `this.share.newPassword = await GeneratePassword()` was executed
before the computed properties where evaluated.

Resolves : https://github.com/nextcloud/server/issues/43919

Signed-off-by: fenn-cs <fenn25.fn@gmail.com>

apps/files_sharing/src/views/SharingDetailsTab.vue

@@ -752,7 +752,7 @@ export default {
 
 			if (this.isNewShare) {
 				if (this.isPasswordEnforced && this.isPublicShare) {
-					this.share.newPassword = await GeneratePassword()
+					this.$set(this.share, 'newPassword', await GeneratePassword())
 					this.advancedSectionAccordionExpanded = true
 				}
 				/* Set default expiration dates if configured */