make recommendation clearer on manifest version mismatch (#54779)

It seems common for people to not infer the recommended action here, so
make it clearer.

base/loading.jl

@@ -2233,15 +2233,16 @@ function collect_manifest_warnings()
  if !isempty(unsuitable_manifests)
  msg *= """
  - Note that the following manifests in the load path were resolved with a different
- julia version, which may be the cause of the error:
+ julia version, which may be the cause of the error. Try to re-resolve them in the
+ current version, or consider deleting them if that fails:
  $(join(unsuitable_manifests, "\n "))
  """
  end
  if !isempty(dev_manifests)
  msg *= """
  - Note that the following manifests in the load path were resolved a potentially
- different DEV version of the current version, which may be the cause
- of the error:
+ different DEV version of the current version, which may be the cause of the error.
+ Try to re-resolve them in the current version, or consider deleting them if that fails:
  $(join(dev_manifests, "\n "))
  """
  end