test: add 1.15~1.20 versions into workflows

[codecov-commenter]

Codecov Report

Merging #608 (cd90902) into master (50d6f22) will decrease coverage by 1.84%. Report is 1596 commits behind head on master. The diff coverage is 70.28%.

:exclamation: Current head cd90902 differs from pull request most recent head 42de565. Consider uploading reports for the commit 42de565 to get more accurate results

@@            Coverage Diff             @@
##           master     #608      +/-   ##
==========================================
- Coverage   95.36%   93.52%   -1.84%     
==========================================
  Files          48       48              
  Lines        2007     2518     +511     
==========================================
+ Hits         1914     2355     +441     
- Misses         50      106      +56     
- Partials       43       57      +14     

Files	Coverage Δ
sdk/auth/credentials/sts_role_arn_credential.go	100.00% <100.00%> (ø)
sdk/auth/roa_signature_composer.go	95.71% <100.00%> (+0.55%)	:arrow_up:
sdk/auth/rpc_signature_composer.go	91.66% <100.00%> (+1.19%)	:arrow_up:
sdk/config.go	100.00% <ø> (ø)
sdk/endpoints/endpoints_config.go	66.66% <ø> (+6.66%)	:arrow_up:
sdk/errors/server_error.go	100.00% <100.00%> (ø)
sdk/logger.go	100.00% <ø> (ø)
sdk/requests/common_request.go	100.00% <100.00%> (ø)
sdk/requests/roa_request.go	97.43% <100.00%> (+0.61%)	:arrow_up:
sdk/responses/response.go	92.85% <100.00%> (+2.15%)	:arrow_up:
... and 5 more

... and 33 files with indirect coverage changes