Update influxdb repo key

[elfranne]

The repo key has been changed: https://www.influxdata.com/blog/linux-package-signing-key-rotation/

https://portal.influxdata.com/downloads/

[...]
Get:6 https://repos.influxdata.com/ubuntu focal InRelease [7.019 B]            
Err:6 https://repos.influxdata.com/ubuntu focal InRelease                      
  The following signatures couldn't be verified because the public key is not available: NO_PUBKEY D8FF8E1F7DF8B07E
Hit:7 https://packagecloud.io/sensu/stable/ubuntu focal InRelease
Reading package lists... Done
W: GPG error: https://repos.influxdata.com/ubuntu focal InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY D8FF8E1F7DF8B07E
E: The repository 'https://repos.influxdata.com/ubuntu focal InRelease' is no longer signed.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.

[MartyEwings]

@elfranne thanks!

[MartyEwings]

@elfranne looks like there are some unit tests that need updated as well, is that something you can add to this PR?

[m0dular]

Works great, thanks 👍 I'll sort the Ubuntu issues in a separate PR