Bump sqlx-cli version to fix its compiling error when installing

backend/scripts/database/init_database.sh

@@ -13,7 +13,7 @@ fi
 if ! [ -x "$(command -v sqlx)" ]; then
   echo >&2 "Error: `sqlx` is not installed."
   echo >&2 "Use:"
-  echo >&2 "    cargo install --version=0.5.5 sqlx-cli --no-default-features --features postgres"
+  echo >&2 "    cargo install --version=^0.5.6 sqlx-cli --no-default-features --features postgres"
   echo >&2 "to install it."
   exit 1
 fi