message: Fix alpha imports in docs/permission/writing-a-policy.md
diff: @@ -53,7 +53,7 @@ Let's change the policy to the following:
  + } from '@backstage/plugin-catalog-backend/alpha';
  + import {
  + catalogEntityDeletePermission,
  -+ } from '@backstage/plugin-catalog-common';
  ++ } from '@backstage/plugin-catalog-common/alpha';
  ...
  @@ -106,7 +106,7 @@ import {
  } from '@backstage/plugin-catalog-backend/alpha';
  - import {
  - catalogEntityDeletePermission,
  -- } from '@backstage/plugin-catalog-common';
  +- } from '@backstage/plugin-catalog-common/alpha';
  ...
  