Use CSV-separated outputs @ get-changed-files @ CI

This is necessary because paths with whitespaces tend to crash said
action[[1]][[2]][[3]]. Also, we don't need to use JSON as it's harder
to parse while the value isn't used except for the emptiness check.

The change fixes [[4]]

[1]: https://github.com/Ana06/get-changed-files#get-all-changed-files-as-space-delimited
[2]: python#103914 (comment)
[3]: python#103914 (comment)
[4]: python#103914 (comment)

Author: webknjaz

.github/workflows/build.yml

@@ -89,6 +89,7 @@ jobs:
             Doc/**
             Misc/**
             .github/workflows/reusable-docs.yml
+          format: csv  # unbreaks paths /w whitespaces; json is harder to parse
       - name: Check for docs changes
         if: >-
           github.event_name == 'pull_request'

.github/workflows/reusable-docs.yml

@@ -40,6 +40,7 @@ jobs:
       uses: Ana06/get-changed-files@v2.2.0
       with:
         filter: "Doc/**"
+        format: csv  # unbreaks paths /w whitespaces; json is harder to parse
     - name: 'Build changed files in nit-picky mode'
       if: github.event_name == 'pull_request'
       continue-on-error: true