ci: Bump rust stable version for twotx build

[joncinque]

Problem

The two-tx build is failing due to unsupported language features, following the bump to rust 1.65 on the monorepo. See https://github.com/solana-labs/solana-program-library/actions/runs/3446859167/jobs/5752258103 for an example

Solution

Bump the version to 1.65 for the twotx build

[joncinque]

@samkim-crypto are these errors expected?

failures:
    ct_configure_token_account
    ct_enable_disable_balance_credits
error: test failed, to rerun pass `--test confidential_transfer`
    ct_new_account_is_empty

[samkim-crypto]

Sorry, I introduced an error while I was cleaning up the ElGamal pubkey derivation in the zk-token-sdk. It is addressed in 28792 and the tests should now pass.