Writing files read via jka-compr overwrites compressed file with uncompressed file

[piater]

Steps to reproduce the behaviour

1. Find any compressed PDF file, say, compr.pdf.gz.
2. Alter it, e.g. by adding annotations.
3. Save it with C-x C-s.

This results in compr.pdf.gz containing the altered PDF, not compressed despite the .gz extension.

Writing to a new file with a .gz extension using C-x -C-w likewise results in an uncompressed file.

What is the expected behaviour?
compr.pdf.gz is replaced by its altered PDF, transparently gzip-compressed by jka-compr.

Your pdf-tools install
Status: Installed in ‘pdf-tools-20230611.239/’ (unsigned).
Version: 20230611.239
Commit: c69e765

This is perhaps best fixed jointly with #258 by changing the file-saving logic of pdf-tools.