Add e2e test about mixedos+flannel

[manuelbuil]

Proposed Changes

Adds support for cni: flannel in the mixedos test

Types of Changes

New test

Verification

E2E_CNI=flannel go test -v -timeout=30m tests/e2e/mixedos/mixedos_test.go

Testing

Linked Issues

User-Facing Change

Further Comments

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 9.82%. Comparing base (71d00cc) to head (ef51ff6).
Report is 30 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #6063       +/-   ##
==========================================
- Coverage   26.10%   9.82%   -16.29%     
==========================================
  Files          32      32               
  Lines        2697    2698        +1     
==========================================
- Hits          704     265      -439     
- Misses       1947    2411      +464     
+ Partials       46      22       -24     

Flag	Coverage Δ
inttests	9.82% <ø> (-0.01%)	⬇️
unittests	?

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[dereknola]

Can you merge the two mixedos e2e test together, and just have CNI be a variable similar to https://github.com/rancher/rke2/blob/master/tests/e2e/validatecluster/Vagrantfile#L10?

[manuelbuil]

Can you merge the two mixedos e2e test together, and just have CNI be a variable similar to https://github.com/rancher/rke2/blob/master/tests/e2e/validatecluster/Vagrantfile#L10?

As long as @ShylajaDevadiga can confirm that we can change that variable in her scripts to run https://rke2-results.s3.us-east-2.amazonaws.com/rke2_ubuntu2004_results.html, then yes :)