[FEATURE-12] Create fpb-diffs.yml workflow

[davorpa]

Description

This workflow runs the parser over current commit of https://github.com/EbookFoundation/free-programming-books project twice:

1. Using the parser at the base commit (aka main)
2. Using the parser at the current commit of the pull_request (aka MERGE_HEAD commit)

Usefull to see how many changes (aka git diff) in fpb.json file introduces a change in the parser. It could act as pseudo-linter.

To mantain it simple I post the results as GitHub Actions summary, but it could be posted as PR comment too.

Context

• A run without changes: https://github.com/davorpa/free-programming-books-parser/actions/runs/3083858729
• A run with changes: https://github.com/davorpa/free-programming-books-parser/actions/runs/3083835412
• Tested PR: Create fpb-diffs.yml workflow davorpa/free-programming-books-parser#1

WITHOUT CHANGES	WITH CHANGES

NOTE:

If this workflow is accepted needs enable GHA environment. Copy same settings from FPB. It seems to be disabled at this moment

[eshellman]

Usefull to see how many changes (aka git diff) in fpb.json file introduces a change in the parser. It could act as pseudo-linter.

Who's going to look at it?

[davorpa]

Usefull to see how many changes (aka git diff) in fpb.json file introduces a change in the parser. It could act as pseudo-linter.

Who's going to look at it?

As you said in #11 (comment) it was useful

Maybe a bit hidden but is responsability of whom review see the changes, or ar least have any tool to automatize it or give facilities.

Do you prefer notify as PR comment or leave it as is with a GHA summary (see runs)?