Update CHANGELOG.md

Author: brandonc

CHANGELOG.md

@@ -1,9 +1,7 @@
-# UNRELEASED
-<!-- Add CHANGELOG entry to this section for any PR awaiting the next release -->
-<!-- Please also include if this is a Bug Fix, Enhancement, or Feature -->
+# v0.51.0
 
 DEPRECATIONS and BREAKING CHANGES:
-* `r/tfe_workspace`: `execution_mode` and `agent_pool_id` attributes have been deprecated in favor of a new resource, `tfe_workspace_settings`. Note that these fields no longer compute defaults which is consistent with using a new resource to manage these same settings. What this means in practice is that if you unset `execution_mode` or `agent_pool_id` without also creating a `tfe_workspace_settings`, the setting will no longer revert to the default "remote" mode. To migrate, relocate the `execution_mode` and `agent_pool_id` arguments to `tfe_workspace_settings`.
+* `r/tfe_workspace`: `execution_mode` and `agent_pool_id` attributes have been deprecated in favor of a new resource, `tfe_workspace_settings`. Note that these fields no longer compute defaults which is consistent with using a new resource to manage these same settings. In practice, this means that if you unset `execution_mode` or `agent_pool_id` without also creating a `tfe_workspace_settings`, the setting will no longer revert to the default "remote" mode. To migrate, relocate the `execution_mode` and `agent_pool_id` arguments to `tfe_workspace_settings`.
 
 BUG FIXES:
 * `r/tfe_policy`: Fix the provider ignoring updates to the `query` field, by @skeggse [1108](https://github.com/hashicorp/terraform-provider-tfe/pull/1108)