Code review comment for autopkgtest-cloud:more-fail-strings

For posterity: we didn't fully understand why in the past the "Temporary failure resolving" error showed up in the logs without --debug, and hence the infinite retry loop was avoided by having that string in FAIL_PKG_STRINGS (assuming that [1] worked as intended in the first place!). This is tracked in LP: #1988223.

In the end we decided the most sensible thing to do is just merging this change.

[1] https://git.launchpad.net/autopkgtest-cloud/commit/?id=625889eb9b6a7a8075e20635df4a6c59fb935eb0