build(forgejo): add push-next job

.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.yml

@@ -0,0 +1,21 @@
+name: Rust
+
+on:
+  push:
+    branches: ["next"]
+  pull_request:
+    branches: ["main"]
+
+env:
+  CARGO_TERM_COLOR: always
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v4
+      - name: Build
+        run: cargo build --verbose
+      - name: Run tests
+        run: cargo test --verbose