Fix YAML linting issues and update system requirements to Debian 13+

- Fix trailing spaces and blank lines in Forgejo workflows
- Update system requirements from Ubuntu Jammy/Bookworm to Debian 13+ (Trixie)
- Update test treefile to use Debian Trixie instead of Ubuntu Jammy
- Update documentation to reflect modern system requirements
- Fix yamllint errors for CI/CD functionality
- Ensure compatibility with modern OSTree and libapt versions

tests/test-treefile.yaml

@@ -1,30 +1,30 @@
 # Test treefile for apt-ostree compose tree
-# This defines a minimal Ubuntu system with apt-ostree
+# This defines a minimal Debian 13+ system with apt-ostree
 
 # OSTree repository configuration
 ostree:
-  ref: apt-ostree/test/ubuntu/22.04
+  ref: apt-ostree/test/debian/trixie
   repo: /tmp/apt-ostree-test/repo
 
 # Base system (required)
-base: ubuntu:22.04
+base: debian:trixie
 
 # APT package sources
 apt:
   sources:
-    - "deb http://archive.ubuntu.com/ubuntu jammy main restricted universe multiverse"
-    - "deb http://archive.ubuntu.com/ubuntu jammy-updates main restricted universe multiverse"
-    - "deb http://archive.ubuntu.com/ubuntu jammy-security main restricted universe multiverse"
+    - "deb http://deb.debian.org/debian trixie main contrib non-free"
+    - "deb http://deb.debian.org/debian trixie-updates main contrib non-free"
+    - "deb http://deb.debian.org/debian trixie-security main contrib non-free"
 
 # Packages to install
 packages:
   # Base system packages
-  - ubuntu-minimal
+  - debian-minimal
   - systemd
   - ostree
   - apt
   - dpkg
-  
+
   # Essential utilities
   - bash
   - coreutils
@@ -32,7 +32,7 @@ packages:
   - wget
   - gnupg
   - ca-certificates
-  
+
   # For testing purposes
   - vim
   - htop
@@ -44,7 +44,7 @@ system:
   services:
     - systemd-networkd
     - systemd-resolved
-  
+
   # Create basic directory structure
   directories:
     - /etc/apt-ostree
@@ -54,4 +54,4 @@ system:
 # Post-installation scripts (optional)
 postinstall:
   - echo "apt-ostree test system created successfully"
-  - echo "OSTree ref: apt-ostree/test/ubuntu/22.04" 
+  - echo "OSTree ref: apt-ostree/test/debian/trixie"