Change to new dev images to fix failing circleci builds.

[chummels]

Circle CI legacy tests have been failing for a while with this error:

Get:1 http://security.debian.org/debian-security buster/updates InRelease [34.8 kB]
Get:2 http://deb.debian.org/debian buster InRelease [122 kB]
Get:3 http://deb.debian.org/debian buster-updates InRelease [56.6 kB]
Reading package lists... Done  
E: Repository 'http://security.debian.org/debian-security buster/updates InRelease' changed its 'Suite' value from 'stable' to 'oldstable'
N: This must be accepted explicitly before updates for this repository can be applied. See apt-secure(8) manpage for details.
N: Repository 'http://deb.debian.org/debian buster InRelease' changed its 'Version' value from '10.5' to '10.12'
E: Repository 'http://deb.debian.org/debian buster InRelease' changed its 'Suite' value from 'stable' to 'oldstable'
N: This must be accepted explicitly before updates for this repository can be applied. See apt-secure(8) manpage for details.
E: Repository 'http://deb.debian.org/debian buster-updates InRelease' changed its 'Suite' value from 'stable-updates' to 'oldstable-updates'
N: This must be accepted explicitly before updates for this repository can be applied. See apt-secure(8) manpage for details.

Exited with code exit status 100
CircleCI received exit code 100

According to this page it appears this can be fixed with the simple change in this PR.