fix: make RPM runtime portable on Tumbleweed

packaging/rpm/post.sh

@@ -5,7 +5,8 @@ set -eu
 STORE_DIR="/var/lib/fenris"
 STORE_DB="${STORE_DIR}/observations.db"
 STORE_BAK="${STORE_DIR}/observations.db.bak"
-VENV_PYTHON="/opt/fenris/bin/python3"
+RUNTIME_PYTHON="/usr/bin/python3"
+VENDOR_DIR="/opt/fenris/vendor"
 
 if [ "$1" -eq 1 ]; then
     # Fresh install
@@ -17,8 +18,8 @@ elif [ "$1" -ge 2 ]; then
     if [ -f "${STORE_DB}" ]; then
         cp "${STORE_DB}" "${STORE_BAK}" 2>/dev/null || true
     fi
-    if [ -x "${VENV_PYTHON}" ] && [ -f "${STORE_DB}" ]; then
-        "${VENV_PYTHON}" -c "
+    if [ -d "${VENDOR_DIR}" ] && [ -f "${STORE_DB}" ]; then
+        PYTHONPATH="${VENDOR_DIR}" "${RUNTIME_PYTHON}" -c "
 from fenris.store import migrate_to_latest
 from pathlib import Path
 n = migrate_to_latest(Path('${STORE_DB}'))