Corrected return type for validators

[gauravgahlot]

Description

The PR fixes the return type for template validation functions.

Reference thread here.

How Has This Been Tested?

Unit tests.

How are existing users impacted? What migration steps/scripts do we need?

No impact.

Checklist:

I have:

• updated the documentation and/or roadmap (if required)
• added unit or e2e tests
• provided instructions on how to upgrade

[codecov]

Codecov Report

Merging #284 into master will decrease coverage by 0.64%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #284      +/-   ##
==========================================
- Coverage   20.61%   19.97%   -0.65%     
==========================================
  Files          15       15              
  Lines        1363     1352      -11     
==========================================
- Hits          281      270      -11     
  Misses       1068     1068              
  Partials       14       14              

Impacted Files	Coverage Δ
pkg/template_validator.go	100.00% <100.00%> (ø)

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