tools/devtool: downgrade parent instance Rust version to 1.60

There is nothing in dependencies of parent instance side that would require
Rust version to be more than 1.60.

Keeping it lower at this moment.

Signed-off-by: Eugene Koira <eugkoira@amazon.com>

tools/devtool

@@ -30,7 +30,7 @@ EVBIN_CLI=p11ne-cli
 EVBIN_INIT=p11ne-init
 EVBIN_P11_MOD=libvtok_p11.so
 
-P11NE_PARENT_RUST_TOOLCHAIN=1.63.0
+P11NE_PARENT_RUST_TOOLCHAIN=1.60.0
 P11NE_ENCLAVE_RUST_TOOLCHAIN=1.63.0
 
 USAGE="\