chore: use testing.TB instead of *testing.T

[katcipis]

Use testing.TB on asserts so they can be used on benchmarks. Also fixes a bug on assert messages.

[codecov]

Codecov Report

Merging #22 (6c55657) into main (600dcdc) will increase coverage by 2.28%.
The diff coverage is 50.00%.

@@            Coverage Diff             @@
##             main      #22      +/-   ##
==========================================
+ Coverage   77.41%   79.69%   +2.28%     
==========================================
  Files          11       11              
  Lines         518      522       +4     
==========================================
+ Hits          401      416      +15     
+ Misses        114      102      -12     
- Partials        3        4       +1     

Flag	Coverage Δ
tests	79.69% <50.00%> (+2.28%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
assert/error.go	18.51% <0.00%> (+18.51%)	⬆️
assert/partial.go	80.00% <0.00%> (ø)
assert/string.go	28.57% <0.00%> (ø)
assert/equal.go	43.05% <16.66%> (+8.33%)	⬆️
assert/assert.go	85.00% <100.00%> (+1.66%)	⬆️

📣 We’re building smart automated test selection to slash your CI/CD build times. Learn more