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MINOR: [R] Update a URL to https

This PR aims to solve some of the `urlchecker::url_check()` findings.
3 complaints from the `urlchecker` are left:
*  Conda forge badge, for which the URL is correct:
```
Error: README.md:5:75 400: Bad Request
[![conda-forge](https://img.shields.io/conda/vn/conda-forge/r-arrow.svg)](https://anaconda.org/conda-forge/r-arrow)
```

* 2 for articles which have not yet been published:
```
x Error: vignettes/developing.Rmd:16:46 404: Not Found
* [running R with the C++ debugger attached](https://arrow.apache.org/docs/r/articles/developers/debugging.html)```
                                             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
x Error: vignettes/install.Rmd:18:33 404: Not Found
[developers' installation docs](https://arrow.apache.org/docs/r/articles/developers/install_details.html)

Closes #12360 from dragosmg/url_update

Authored-by: Dragoș Moldovan-Grünfeld <dragos.mold@gmail.com>
Signed-off-by: Neal Richardson <neal.p.richardson@gmail.com>