[ci] Temporarily disable kubeval validation

[schallert]

Kubeval depends on hashicorp/go-multierror, which now depends on
go1.13 error methods.

What this PR does / why we need it:

Fixes #

Special notes for your reviewer:

Does this PR introduce a user-facing and/or backwards incompatible change?:

Does this PR require updating code package or user-facing documentation?:

[codecov]

Codecov Report

Merging #2241 into master will decrease coverage by 0.2%.
The diff coverage is n/a.

@@           Coverage Diff            @@
##           master   #2241     +/-   ##
========================================
- Coverage    72.6%   72.4%   -0.3%     
========================================
  Files        1024    1024             
  Lines       89710   89129    -581     
========================================
- Hits        65174   64533    -641     
- Misses      20162   20248     +86     
+ Partials     4374    4348     -26     

Flag	Coverage Δ
#aggregator	82.0% <ø> (-0.1%)	⬇️
#cluster	85.2% <ø> (ø)
#collector	82.8% <ø> (ø)
#dbnode	79.0% <ø> (-0.3%)	⬇️
#m3em	74.1% <ø> (-0.3%)	⬇️
#m3ninx	74.4% <ø> (ø)
#m3nsch	51.1% <ø> (ø)
#metrics	17.5% <ø> (ø)
#msg	74.9% <ø> (ø)
#query	68.8% <ø> (-0.7%)	⬇️
#x	83.2% <ø> (ø)

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[robskillington]

LGTM

[schallert]

Ref #2220