git: Added Flatpak CI

.github/workflows/build.yml

@@ -1129,6 +1129,61 @@ jobs:
           name: Snap ${{ matrix.architecture }}
           path: ${{ steps.snapcraft.outputs.snap }}
 
+  flatpak-build:
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - architecture: "x86_64"
+            flatpak_arch: "x86_64"
+            image: ubuntu-24.04
+          - architecture: "arm64"
+            flatpak_arch: "aarch64"
+            image: ubuntu-24.04-arm
+    name: 🐧 Flatpak ${{ matrix.architecture }}
+    runs-on: ${{ matrix.image }}
+
+    permissions:
+      id-token: write
+      attestations: write
+
+    steps:
+      - name: ⬇️ Install setup dependencies
+        run: |
+          sudo apt update && sudo apt install -y git curl flatpak-builder
+
+      - name: 🧰 Checkout
+        uses: actions/checkout@v4
+        with:
+          submodules: recursive
+
+      - name: 📜 Set version variable
+        run: |
+          echo "IMHEX_VERSION=`cat VERSION`" >> $GITHUB_ENV
+
+      - name: 🛠️ Build
+        uses: flatpak/flatpak-github-actions/flatpak-builder@v6
+        with:
+          bundle: imhex-${{ env.IMHEX_VERSION }}-${{ matrix.architecture }}.flatpak
+          manifest-path: dist/flatpak/net.werwolv.ImHex.yaml
+          cache-key: flatpak-builder-${{ matrix.architecture }}-${{ github.sha }}
+          arch: ${{ matrix.flatpak_arch }}
+
+      - name: 🗝️ Generate build provenance attestations
+        uses: actions/attest-build-provenance@v2
+        if: ${{ github.event.repository.fork == false && github.event_name != 'pull_request' }}
+        with:
+          subject-path: |
+            imhex-${{ env.IMHEX_VERSION }}-${{ matrix.architecture }}.flatpak
+
+      - name: ⬆️ Upload Flatpak
+        uses: actions/upload-artifact@v4
+        with:
+          if-no-files-found: error
+          name: ${{ matrix.name }} ${{ matrix.release_num }} Flatpak ${{ matrix.architecture }}
+          path: |
+            imhex-${{ env.IMHEX_VERSION }}-${{ matrix.architecture }}.flatpak
+
   webassembly-build:
     runs-on: ubuntu-24.04
     name: 🌍 Web