CHANGELOG: Add entry for breaking change to curve22519-dalek crate (#…

…3335)

CHANGELOG: Add entry for breaking change to curve22519-dalek

#### Problem

#1693 introduced a breaking change between v2.0 and v2.1 of the Solana
crates by bumping a dependency to a new major version, but it isn't
reflected in the changelog.

#### Summary of changes

Add a line in the changelog about the breaking change.

CHANGELOG.md

@@ -20,6 +20,7 @@ Release channels have their own copy of this changelog:
   * SDK:
     * `cargo-build-sbf` and `cargo-build-bpf` have been deprecated for two years and have now been definitely removed.
        Use `cargo-build-sbf` and `cargo-test-sbf` instead.
+    * dependency: `curve25519-dalek` upgraded to new major version 4 (#1693). This causes breakage when mixing v2.0 and v2.1 Solana crates, so be sure to use all of one or the other. Please use only crates compatible with v2.1.
   * Stake:
     * removed the unreleased `redelegate` instruction processor and CLI commands (#2213)
   * Banks-client: