Clone TLS conf in newClient

[betamos]

Fixes #3394

• I searched for other potential places in non-tests where this was happening, and this is the only one I found. In other places, it's appropriately cloned already.
• I took a look at the unit tests, but it seems out of place with a specific client test in that file given the harness (BeforeEach) and the other tests. Also it would be very fragile to changes, and likely not catch other instances. I'd recommend taking a look at running integration tests with -race in case you're not already doing that. Or let me know if you already a unit test approach in mind.

Obligatory thanks for maintaining this amazing library.

[google-cla]

Thanks for your pull request! It looks like this may be your first contribution to a Google open source project. Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

For more information, open the CLA check for this pull request.

[marten-seemann]

LGTM. Thank you @betamos!

Can you please sign the CLA? Then we can merge the PR.

[codecov]

Codecov Report

Merging #3400 (b8f0373) into master (5dedb7e) will decrease coverage by 0.01%.
The diff coverage is 50.00%.

@@            Coverage Diff             @@
##           master    #3400      +/-   ##
==========================================
- Coverage   85.36%   85.36%   -0.01%     
==========================================
  Files         135      135              
  Lines        9928     9930       +2     
==========================================
+ Hits         8475     8476       +1     
  Misses       1068     1068              
- Partials      385      386       +1     

Impacted Files	Coverage Δ
client.go	78.91% <50.00%> (-0.46%)	⬇️

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[betamos]

Can you please sign the CLA?

I did earlier today. Verified that email matches commit and username is correct. Is it possible to re-run the workflow? Otherwise, I don't know what could be the issue.

[marten-seemann]

@lucas-clemente Can you please check? Looks like the CLA bot is misbehaving (again).

[betamos]

I was able to retrigger the CLA check myself, there was a link at the bottom that I missed the first time around.

Good to go now :)