Upgrade Solana to 1.18.8

[acheroncrypto]

Problem

Solana v1.18 is required to build newer programs but we weren't able to upgrade the repository (#2795) due to program memory related bugs (anza-xyz/agave#252). The issues have been fixed in anza-xyz/agave#362 and was included in v1.18.8 release.

MSRV error with previous toolchain versions:

$ anchor build
error: package `solana-program v1.18.8` cannot be built because it requires rustc 1.75.0 or newer, while the currently active rustc version is 1.72.0-dev
Either upgrade to rustc 1.75.0 or newer, or use
cargo update -p solana-program@1.18.8 --precise ver
where `ver` is the latest version of `solana-program` supporting rustc 1.72.0-dev

Solution

Upgrade Solana tools to 1.18.8.

[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.

[acheroncrypto]

The spl-token-2022 errors we have in CI looks to be related with upgradeable program clones in general. I created upstream issue (anza-xyz/agave#436) to track this.