fix: etcd scheme on grpc resolver

[kevwan]

1. because resolver logic changed in grpc new versions
2. after idle, grpc close the builder and call Build method again

[codecov]

Codecov Report

Attention: Patch coverage is 61.11111% with 7 lines in your changes missing coverage. Please review.

Project coverage is 95.09%. Comparing base (8690859) to head (7a970e7).
Report is 128 commits behind head on master.

Files	Patch %	Lines
zrpc/resolver/internal/discovbuilder.go	64.70%	6 Missing ⚠️
zrpc/resolver/internal/kubebuilder.go	0.00%	1 Missing ⚠️

Additional details and impacted files

Files	Coverage Δ
zrpc/resolver/internal/kubebuilder.go	16.07% <0.00%> (-4.69%)	⬇️
zrpc/resolver/internal/discovbuilder.go	51.42% <64.70%> (+12.96%)	⬆️

... and 253 files with indirect coverage changes