Update version to v1.18.4

[willhickey]

Nothing in this changeset except the version bump:

$ glol -2
7eddaee93c 2024-02-23 22:52:53 -0600  (HEAD -> version_bump_v1.18.4)  [email protected] Revert proc-macro-crate version changes
d97ea6b59a 2024-02-23 22:38:51 -0600  (origin/version_bump_v1.18.4)  [email protected] Update version to v1.18.4
$ git diff v1.18..HEAD | grep -vE "^ |^@@ |^--- |^\+\+\+ |^index |^diff |^-( \")?solana.*1.18.3|^\+( \")?solana.*1.18.4|^-version|^\+version"
$

[mergify]

automerge label removed due to a CI failure