spl: Pin version of toml_edit crate to 0.21.0

[acheroncrypto]

Problem

New installations of anchor-spl come with toml_edit 0.21.1 which has a MSRV of 1.69 which results in the following error when using solana-cli 1.17:

error: package `toml_edit v0.21.1` cannot be built because it requires rustc 1.69 or newer, while the currently active rustc version is 1.68.0-dev

There is also no good reason for a program to depend on toml_edit crate but that's not something we have control over since it's a transitive dependency of spl-token-2022.

Related: solana-labs/solana#33504

Summary of changes

Use fixed version toml_edit = "=0.21.0" in anchor-spl to block cargo from fetching the newest version.

This is necessary until #2795 is merged but that also has its own problems.

[vercel]

@acheroncrypto is attempting to deploy a commit to the coral-xyz Team on Vercel.

A member of the Team first needs to authorize it.

[Dammi87]

Leaving this here in case somebody has this issue and is looking for a quick resolution.
I first built my program - it generated the Cargo.lock file and reported the error. In pure irritation I opened Cargo.lock file and removed the damn toml_edit 0.21.0 entry, it seems to generate the 0.19.15 entry for me so that made me think to simply remove the other one.

This got me passed the error and I could build just fine as before.

NOTE: This is literally my second week in Rust, I have no idea what I'm doing