update workflows

Author: mimmi20

.github/workflows/continuous-integration.yml

@@ -62,6 +62,7 @@ jobs:
       skip-eslint: true
       skip-stylelint: true
       skip-prettier: true
+      skip-libpng-install: true
       phpcs-options: ""
 
   tests:

.github/workflows/lint-workflow-files.yml

@@ -14,6 +14,7 @@ jobs:
     with:
       skip-nasm-install: false
       skip-libimagequant-install: false
+      skip-libpng-install: true
 
   # This is a meta job to avoid to have to constantly change the protection rules
   # whenever we touch the matrix.