CI: Move the flatpak build steps to their own job

This is entirely a GitHub limitation. But I have found myself wanting to
rerun flaky CI tests, but have to wait some time for the flatpak builder
to complete. Moving this to its own job means we don't need to wait to
restart other CI jobs.

.github/workflows/ci.yml

@@ -74,23 +74,3 @@ jobs:
       arch: ${{ matrix.arch }}
       build_preset: ${{ matrix.build_preset }}
       clang_plugins: ${{ matrix.clang_plugins }}
-
-  Flatpak:
-    if: github.repository == 'LadybirdBrowser/ladybird'
-    name: Flatpak ${{ matrix.arch }}
-
-    strategy:
-      fail-fast: false
-      matrix:
-        arch: ['x86_64']
-        runner_labels: ['["blacksmith-16vcpu-ubuntu-2404"]']
-
-        include:
-          - arch: 'aarch64'
-            runner_labels: '["blacksmith-16vcpu-ubuntu-2404-arm"]'
-
-    secrets: inherit
-    uses: ./.github/workflows/flatpak-template.yml
-    with:
-      arch: ${{ matrix.arch }}
-      runner_labels: ${{ matrix.runner_labels }}

.github/workflows/flatpak.yml

@@ -0,0 +1,28 @@
+name: Flatpak
+
+on: [push, pull_request]
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.head_ref || format('{0}-{1}', github.ref, github.run_number) }}
+  cancel-in-progress: true
+
+jobs:
+  Flatpak:
+    if: github.repository == 'LadybirdBrowser/ladybird'
+    name: Flatpak ${{ matrix.arch }}
+
+    strategy:
+      fail-fast: false
+      matrix:
+        arch: ['x86_64']
+        runner_labels: ['["blacksmith-16vcpu-ubuntu-2404"]']
+
+        include:
+          - arch: 'aarch64'
+            runner_labels: '["blacksmith-16vcpu-ubuntu-2404-arm"]'
+
+    secrets: inherit
+    uses: ./.github/workflows/flatpak-template.yml
+    with:
+      arch: ${{ matrix.arch }}
+      runner_labels: ${{ matrix.runner_labels }}