Make build job names more descriptive (#2657)

Previously every build showed up in the CI as "build".

Update the job names to reflect what they are. For example the Ubuntu
build is now called "ubuntu_build"

Co-authored-by: Patrick <tingping@tingping.se>

.github/workflows/flatpak-build.yml

@@ -1,7 +1,7 @@
 name: Flatpak Build
 on: [push, pull_request]
 jobs:
-  build:
+  flatpak_build:
     runs-on: ubuntu-latest
     container:
       image: bilelmoussaoui/flatpak-github-actions:gnome-40