Update agent-policy.md (#6192)

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Co-authored-by: Visha Angelova <91186315+vishaangelova@users.noreply.github.com>

Author: jamie-wilson88

reference/fleet/agent-policy.md

@@ -202,7 +202,7 @@ To edit a custom field:
 2. Click the **Settings** tab and scroll to **Custom fields**. Any custom fields that have been configured are shown.
 3. Click the edit icon to update a field or click the delete icon to remove it.
 
-Adding custom tags is not supported for a small set of inputs:
+Adding custom fields is not supported for a small set of inputs:
 
 * `apm`
 * `cloudbeat` and all `cloudbeat/*` inputs