debug: try rustup update and 'stable' in CI build

Author: yujiyokoo

mise.toml

@@ -548,7 +548,9 @@ fi
 {% endif %}
 
 # cross-compile
-rustup target add --toolchain 1.87.0 {{ target }}
+rustup update
+
+rustup target add --toolchain stable {{ target }}
 
 cargo build --locked --target {{ target }} --release --package cipherstash-proxy