[OS X Emacs] Can't update packages

[Devin Caughey]

Hello,

I am using Aquamacs 3.5 with Mac OS 11.2.3, and I have been unable to update or install packages for some time. For example, running `M-x package-list-packages` on a vanilla (no customizations) version of Aquamacs yields the following messages:
```
Importing package-keyring.gpg...done
Setting ‘package-selected-packages’ temporarily since "emacs -q" would overwrite customizations
error in process filter: Error retrieving: https://melpa.org/packages/archive-contents (error http 400) [2 times]
error in process filter: Error retrieving: https://stable.melpa.org/packages/archive-contents (error http 400) [2 times]
Package refresh done
9 packages can be upgraded; type ‘⇧U’ to mark them for upgrading.
error in process filter: package--check-signature-content: Failed to verify signature: "archive-contents.sig"
error in process filter: Failed to verify signature: "archive-contents.sig"
```
as well as the following error:
```
Failed to verify signature archive-contents.sig:
No public key for 066DAFCB81E42C40 created at 2021-03-28T17:15:02-0400 using RSA
Command output:
gpg: Signature made Sun Mar 28 17:15:02 2021 EDT
gpg:                using RSA key C433554766D3DDC64221BFAA066DAFCB81E42C40
gpg: Can't check signature: No public key
```

Per this link <https://github.com/aquamacs-emacs/aquamacs-emacs/issues/133#issuecomment-337085534>, I tried adding the lines
```
(require 'tls)
(push "/usr/local/etc/libressl/cert.pem" gnutls-trustfiles)
```
to my Preferences.el file and the same thing happens.

Any help would be appreciated. Thanks!
Devin