chore: don't run unattended upgrade if using "no outbound" test feature

[jackfrancis]

Reason for Change:

This PR ensures that when we're using the "block outbound internet access" test feature flag, we don't try to run unattended-upgrade as a blocking CSE operation (which will never finish due to default apt servers not being reachable).

Issue Fixed:

Credit Where Due:

Does this change contain code from or inspired by another project?

• No
• Yes

If "Yes," did you notify that project's maintainers and provide attribution?

• No
• Yes

Requirements:

• uses conventional commit messages
• includes documentation
• adds unit tests
• tested upgrade from previous version

Notes:

[Michael-Sinz]

/lgtm

[acs-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: jackfrancis, Michael-Sinz

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[codecov]

Codecov Report

Merging #4297 (e4ec1f1) into master (77f6aa2) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #4297   +/-   ##
=======================================
  Coverage   72.03%   72.03%           
=======================================
  Files         141      141           
  Lines       21633    21633           
=======================================
  Hits        15584    15584           
  Misses       5099     5099           
  Partials      950      950           

Impacted Files	Coverage Δ
pkg/engine/templates_generated.go	43.56% <ø> (ø)

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