Add 1.18.x and 1.19.x unit tests

[aimuz]

Add 1.18.x and 1.19.x unit tests

[codecov-commenter]

Codecov Report

Base: 84.01% // Head: 58.74% // Decreases project coverage by -25.26% ⚠️

Coverage data is based on head (af00985) compared to base (6e2c2ac).
Patch coverage: 50.91% of modified lines in pull request are covered.

Additional details and impacted files

@@             Coverage Diff             @@
##               v2     #513       +/-   ##
===========================================
- Coverage   84.01%   58.74%   -25.27%     
===========================================
  Files          30       31        +1     
  Lines         932     1583      +651     
===========================================
+ Hits          783      930      +147     
- Misses        110      590      +480     
- Partials       39       63       +24     

Impacted Files	Coverage Δ
chain.go	0.00% <ø> (-90.91%)	⬇️
interceptors/auth/auth.go	100.00% <ø> (ø)
interceptors/ratelimit/ratelimit.go	60.00% <0.00%> (-40.00%)	⬇️
interceptors/recovery/options.go	78.57% <ø> (ø)
metadata/single_key.go	60.00% <ø> (ø)
testing/testpb/interceptor_suite.go	0.00% <0.00%> (ø)
testing/testpb/test.manual_validator.pb.go	0.00% <0.00%> (ø)
util/backoffutils/backoff.go	60.00% <ø> (ø)
wrappers.go	66.66% <ø> (-33.34%)	⬇️
interceptors/reporter.go	45.45% <20.00%> (-17.05%)	⬇️
... and 28 more

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[johanbrandhorst]

Lets drop tests for 1.15 and 1.16 while we're at it. Thanks!

[johanbrandhorst]

Thanks for your contribution!