chore: update Linux VHDs to 2021.04.13

[jackfrancis]

Reason for Change:

This PR updates the Linux VHDs to the 2021.04.13 version in preparation for a v0.62.0 release.

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:

[acs-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: jackfrancis

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• OWNERS [jackfrancis]

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[codecov]

Codecov Report

Merging #4366 (923ef5c) into master (3445c1b) will decrease coverage by 0.03%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #4366      +/-   ##
==========================================
- Coverage   72.08%   72.04%   -0.04%     
==========================================
  Files         141      141              
  Lines       21667    21631      -36     
==========================================
- Hits        15618    15584      -34     
+ Misses       5097     5096       -1     
+ Partials      952      951       -1     

Impacted Files	Coverage Δ
pkg/engine/templates_generated.go	43.31% <0.00%> (-0.25%)	⬇️
pkg/api/addons.go	98.01% <0.00%> (-0.03%)	⬇️
pkg/engine/artifacts.go	98.88% <0.00%> (-0.03%)	⬇️
pkg/api/k8s_versions.go	100.00% <0.00%> (ø)
pkg/api/vlabs/validate.go	81.83% <0.00%> (+0.05%)	⬆️

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