Do not allow RSA signatures with SHA1 algorithms

[alexgg]

openssh v8.8 has deprecated SHA1 algorithms for RSA - however the backend VPN still uses them. Once that is no longer the case the change in df5e9dc can be reverted.

(internal) https://balena.zulipchat.com/#narrow/stream/345889-loop.2Fbalena-os/topic/generic.20x86.20test.20failues

[ycardaillac]

Hello,

We are currently in the process of cleaning up our issues.

This one is (hopefully) not an issue anymore.

Bests,

Yann

[alexgg]

This is still very much an issue still.