Bump Unity package version to 1.2.1 (#334)

## Description of Changes
Missed in
#333.

We should update the 1.2.1 tag and the `release/latest` branch after
this.

## API

 - [ ] This is an API breaking change to the SDK

Nope

## Requires SpacetimeDB PRs
None

## Testsuite
SpacetimeDB branch name: master

## Testing
CI only

Co-authored-by: Zeke Foppa <bfops@users.noreply.github.com>

Author: bfops

package.json

@@ -1,7 +1,7 @@
 {
   "name": "com.clockworklabs.spacetimedbsdk",
   "displayName": "SpacetimeDB SDK",
-  "version": "1.2.0",
+  "version": "1.2.1",
   "description": "The SpacetimeDB Client SDK is a software development kit (SDK) designed to interact with and manipulate SpacetimeDB modules..",
   "keywords": [],
   "author": {