Add note about the fix from upgrading go-slug

Upgrading go-tfe pulled in this update for free, but it fixes a user-facing bug
in the provider that deserves mention.

CHANGELOG.md

@@ -8,6 +8,9 @@ FEATURES:
 * `r/tfe_workspace`: Add `auto_apply_run_trigger` attribute, by @nfagerlund [1123](https://github.com/hashicorp/terraform-provider-tfe/pull/1123)
 * `d/tfe_workspace`: Add `auto_apply_run_trigger` attribute, by @nfagerlund [1123](https://github.com/hashicorp/terraform-provider-tfe/pull/1123)
 
+BUG FIXES:
+* Fixed `tfe_policy_set` detecting changes on every run when providing file contents with `tfe_slug`. This may require an updated version of tfc-agent for the full fix to take effect. Fixed by upgrading go-slug to v0.13.1 [1123](https://github.com/hashicorp/terraform-provider-tfe/pull/1123)
+
 ## v0.49.2 (October 4, 2023)
 
 BUG FIXES: