Add test update toolchain workflow

Author: nyonson

.github/workflows/update-toolchains.yml

@@ -0,0 +1,17 @@
+name: Update Toolchains
+
+on:
+  workflow_dispatch:
+  schedule:
+    - cron: '0 0 * * 7'
+
+permissions:
+  contents: write
+  pull-requests: write
+
+jobs:
+  update-stable:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: rust-bitcoin/rust-bitcoin-maintainer-tools/.github/actions/update-stable@master