docs(guides): update ibis-for-dplyr-users.ipynb with latest

[amoeba]

Fixes #6125

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[amoeba]

Hey @cpcloud or @gforsyth can you take a look here? As I mentioned in #6125, I totally messed up my squash and didn't catch my mistake until #6050 was merged. I've successfully pulled the correct copy out of the reflog. While reviewing locally, I found a few issues which are also included here:

• The TOC was actually broken and I hadn't noticed so not all headers were showing. I found the cause and fixed it so all headers show in the TOC
• The breaking change introduced in 3caf3a1 that changes how suffixes work in joins affected this notebook and I've updated the text and code to match the new behavior
• I updated two headers to match the same style as the previous ones so the headers are all consistent now
• One cell had slightly quirky formatting which I've fixed

I don't think any of these changes will be controversial. I've checked that the output is right locally and on ReviewNB. Sorry for the mistake in the first place.

[cpcloud]

@amoeba This looks really great! Thanks for following up.

Couple of micronits, but nothing blocking.

[amoeba]

Thanks @cpcloud, left you one followup question.

[cpcloud]

Thanks @amoeba !