bug#38494: 25.2.2 gpg error upon listing packages; auctex not located in repos

[AC]

For what it's worth, this has been broken on Ubuntu 18.04 for just about ever.. 
On all of my Ubuntu machines I simply build the emacs-27 branch from source[0]. 

It's been working fine for months (I forget when the problem first manifested). 

---

References:

[0] https://savannah.gnu.org/git/?group=emacs

On August 2, 2020 6:14:10 AM EDT, Lars Ingebrigtsen <larsi@gnus.org> wrote:
>Stuart Little <achirvasub@gmail.com> writes:
>
>> I'm running Ubuntu 18.04.3 LTS, with that distro's standard emacs
>distribution, 25.2.2.
>>
>> Problem: running
>>
>> M-x package-list-packages
>>
>> results in a gpg error:
>>
>> --- cut here ---
>>
>> Failed to verify signature archive-contents.sig:
>> No public key for 066DAFCB81E42C40 created at
>2019-12-02T18:00:02-0500 using RSA
>> Command output:
>> gpg: Signature made Mon 02 Dec 2019 06:00:02 PM EST
>> gpg:                using RSA key
>C433554766D3DDC64221BFAA066DAFCB81E42C40
>> gpg: Can't check signature: No public key
>>
>> --- done ---
>
>I can reproduce this on an 18.04 LTS.  emacs -Q:
>
>Failed to verify signature archive-contents.sig:
>No public key for 066DAFCB81E42C40 created at 2020-08-02T09:05:02+0000
>using RS\
>A
>Command output:
>gpg: Signature made Sun Aug  2 09:05:02 2020 UTC
>gpg:                using RSA key
>C433554766D3DDC64221BFAA066DAFCB81E42C40
>gpg: Can't check signature: No public key
>
>But I vaguely recall that there was something about an expiring key
>that
>made things not work?  In that case, there isn't much to be done here.
>
>Does anybody remember?