Pub/Sub: reformat code to follow style guide

[anguillanneuf]

In a recent #2555, black introduced format changes that don't conform to Google's style guide.

• Use single quotes instead of double quotes
• etc.

Please update the code in the Pub/Sub subdirectory so they are standardized across the entire repo.

[andrewferlitsch]

@anguillanneuf PTAL

[anguillanneuf]

@andrewferlitsch I haven't looked it this issue for some while.

Do you know what's the magic formatting command(s) that let all samples 1) pass all lint tests 2) conform to all formatting style guide?

[leahecole]

I'm going to close this for now because right now, black is the best thing we have for auto-formatting, and pub/sub passes lint regularly, so I am not too worried. However, if you do notice that lint rules look off in the noxfile-template, please let me know. I know @gguuss had a lot of opinions about the style when #2555 first came around, but given that we have not come up with a better solution between the time this issue was opened and now, I don't think it's worth leaving this open. Happy to be contradicted with good reason though, Tianzi! :)