tests: address instabilities, bump kubectl & helm, misc

[jgehrcke]

A small collection of test suite improvements:

• Address three test instabilities: ci instability: 'confirm CD status cleanup' failed with output does not contain substring #901, ci instability: DynMIG: inspect device attributes failed with Cannot iterate over null #902, ci instability: static MIG tests: mig_ensure_teardown_on_all_nodes may fail with "In use by another client" #907
• May improve upon instability ci instability: iupgrade_wait: timeout: sending signal TERM to command 'helm' #895 by bumping the helm CLI from 3.x to 4.x (which changes the way helm waits)
• Bump kubectl used in the test suite
• Add small test suite debuggability improvements
• Increase test coverage in GHA CI (add a test to the subset of tests executed in GHA CI)

[jgehrcke]

I'd like to land this quickly so that the next scheduled run on main can take advantage.