InterceptorTestSuite client connection optimize

[HUSTtoKTH]

The clientConn is not saved and closed with TearDownSuite.

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[yashrsharma44]

LGTM, let's wait for test approval

[codecov-commenter]

Codecov Report

Merging #455 (bfdc5f9) into v2 (6e2c2ac) will decrease coverage by 26.43%.
The diff coverage is 48.07%.

@@             Coverage Diff             @@
##               v2     #455       +/-   ##
===========================================
- Coverage   84.01%   57.58%   -26.44%     
===========================================
  Files          30       28        -2     
  Lines         932     1530      +598     
===========================================
+ Hits          783      881       +98     
- Misses        110      586      +476     
- Partials       39       63       +24     

Impacted Files	Coverage Δ
chain.go	0.00% <ø> (-90.91%)	⬇️
interceptors/auth/auth.go	100.00% <ø> (ø)
interceptors/auth/metadata.go	100.00% <ø> (ø)
interceptors/ratelimit/ratelimit.go	60.00% <0.00%> (-40.00%)	⬇️
interceptors/recovery/options.go	78.57% <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)
util/metautils/single_key.go	60.00% <ø> (ø)
wrappers.go	66.66% <ø> (-33.34%)	⬇️
... and 29 more

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[HUSTtoKTH]

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Corporate signers

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[HUSTtoKTH]

@googlebot I fixed it.

[yashrsharma44]

Thanks for the fix ❤️