ci: publish releases to flakehub

.github/workflows/release.yml

@@ -4,6 +4,12 @@ on:
   push:
     tags:
       - v[0-9]+.[0-9]+.[0-9]+
+  workflow_dispatch:
+    inputs:
+      tag:
+        description: The existing tag to publish to FlakeHub
+        type: string
+        required: true
 
 jobs:
   create_release:
@@ -19,6 +25,7 @@ jobs:
     name: release
     needs: create_release
     runs-on: ${{ matrix.os }}
+    if: github.event_name != 'workflow_dispatch'
     strategy:
       matrix:
         include:
@@ -58,6 +65,7 @@ jobs:
     name: artifacts
     needs: create_release
     runs-on: ubuntu-latest
+    if: github.event_name != 'workflow_dispatch'
 
     steps:
       - name: Checkout
@@ -82,3 +90,18 @@ jobs:
           tag: ${{ github.ref }}
           file: artifacts/*
           file_glob: true
+
+  flakehub:
+    runs-on: ubuntu-latest
+    permissions:
+      id-token: write
+      contents: read
+    steps:
+      - uses: actions/checkout@v3
+        with:
+          ref: ${{ inputs.tag != null && format('refs/tags/{0}', inputs.tag) || '' }}
+      - uses: DeterminateSystems/nix-installer-action@v4
+      - uses: DeterminateSystems/flakehub-push@v3
+        with:
+          visibility: public
+          tag: ${{ inputs.tag }}