build(forgejo): add push-next job

Has both on-docker and on-builder variants while I workout which I can
get to work.

.forgejo/workflows/demo.yaml

@@ -1,6 +0,0 @@
-on: [push]
-jobs:
-  test:
-    runs-on: docker
-    steps:
-      - run: echo All Good Now

.forgejo/workflows/push-next-on-builder.yml

@@ -0,0 +1,24 @@
+name: Rust
+
+on:
+  push:
+    branches: ["next"]
+  pull_request:
+    branches: ["main"]
+
+env:
+  CARGO_TERM_COLOR: always
+
+jobs:
+  build:
+    runs-on: git-next-builder
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Build
+        run: cargo build --verbose
+
+      - name: Run tests
+        run: cargo test --verbose

.forgejo/workflows/push-next-on-docker.yml

@@ -0,0 +1,52 @@
+name: Rust
+
+on:
+  push:
+    branches: ["next"]
+  pull_request:
+    branches: ["main"]
+
+env:
+  CARGO_TERM_COLOR: always
+
+jobs:
+  build:
+    runs-on: docker
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Toolchain
+        uses: https://github.com/actions-rs/toolchain@v1
+        with:
+          toolchain: stable
+
+      - name: Format
+        uses: https://github.com/actions-rs/cargo@v1
+        with:
+          command: fmt
+          args: --all -- --check
+
+      - name: Update apt
+        run: apt-get update
+
+      - name: Install linkers
+        run: apt-get install -y clang-15 mold
+
+      - name: Clippy
+        uses: https://github.com/actions-rs/cargo@v1
+        with:
+          command: clippy
+          args: -- -D warnings
+
+      - name: Build
+        uses: https://github.com/actions-rs/cargo@v1
+        with:
+          command: build
+          # args: --release --all-features
+
+      - name: Test
+        uses: https://github.com/actions-rs/cargo@v1
+        with:
+          command: test