chore(mobile): add isar lock file (#12705)

mobile/scripts/fdroid_update_isar.sh

@@ -0,0 +1,14 @@
+#!/usr/bin/env sh
+
+isar_version="$(awk '/isar: /{gsub(/\^/, "", $2); print $2}' pubspec.yaml)"
+checked_out_version="$(git -C .isar describe --tags)"
+
+if [ "$isar_version" = "$checked_out_version" ]; then
+  echo "isar is up-to-date."
+  exit 0
+fi
+echo "Updating from version $checked_out_version to $isar_version."
+
+git -C .isar checkout "$isar_version"
+cargo generate-lockfile --manifest-path .isar/Cargo.toml
+mv .isar/Cargo.lock .isar-cargo.lock