Update schnorrkel to 0.7.0 (#3261)

* Update schnorrkel to `0.7.0`

* Apply suggestions from code review

Co-Authored-By: DemiMarie-parity <48690212+DemiMarie-parity@users.noreply.github.com>

* Increase `spec_version`

substrate/node/runtime/src/lib.rs

@@ -79,8 +79,8 @@ pub const VERSION: RuntimeVersion = RuntimeVersion {
 	// and set impl_version to equal spec_version. If only runtime
 	// implementation changes and behavior does not, then leave spec_version as
 	// is and increment impl_version.
-	spec_version: 123,
-	impl_version: 125,
+	spec_version: 124,
+	impl_version: 124,
 	apis: RUNTIME_API_VERSIONS,
 };