Optimize PSYDAC logo (#570)

Change the way we color the background of our logo and remove some invisible
layers. This reduces the file size by a lot, e.g. the banner went down from
7 MB to 64 KB. The changes are mostly visible in bright mode.

---------

Co-authored-by: Yaman Güçlü <yaman.guclu@gmail.com>

Author: FrederikSchnack

.github/workflows/testing.yml

@@ -15,10 +15,6 @@ on:
     branches: [ devel, main ]
     types:
       - ready_for_review
-    paths:
-      - 'psydac/**'
-      - 'pytest.ini'
-      - 'pyproject.toml'
 
   workflow_dispatch:
 

CHANGELOG.md

@@ -8,11 +8,13 @@ All notable changes to this project will be documented in this file.
 
 ### Fixed
 
--   #565 Expand editable install info in `README.md`
--   #566 Fix command `psydac test --mpi` on Ubuntu machines
+-   #570 : Optimize PSYDAC logo
+-   #565 : Expand editable install info in `README.md`
+-   #566 : Fix command `psydac test --mpi` on Ubuntu machines
 
 ### Changed
 
+-   [DEVELOPER] Do not check file changes to trigger testing workflow on PRs
 -   [DEVELOPER] Run documentation workflow whenever `README.md` is modified
 -   [DEVELOPER] Run testing workflow on PRs only when set to "ready for review"