Switch coverage build to Trixie

The build didn't fail but also didn't record anything, the newer
versions on my systems work. I'm using Trixie instead of Sid so we'll
be automatically back to stable when Trixie is released.

.github/workflows/build.yaml

@@ -54,7 +54,7 @@ jobs:
 
   coverage:
     runs-on: ubuntu-latest
-    container: debian:bookworm
+    container: debian:trixie
     name: coverage
     steps:
       - uses: actions/checkout@v4