ci: add workflow for reporting possible state-changing diffs

The workflow uses the new github.com/orijtech/statediff tool that
builds a callgraph from a set of root methods and functions, and
checks whether a patch touches it.

Fixes #13518

Signed-off-by: Elias Naur <elias@orijtech.com>

.github/workflows/statediff.yml

@@ -0,0 +1,21 @@
+name: "Warn on state changes"
+
+on:
+  pull_request_target:
+    types:
+      - opened
+      - edited
+      - synchronize
+
+permissions:
+  contents: read
+
+jobs:
+  main:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - uses: orijtech/statediff@main
+        with:
+          roots: 'github.com/cosmos/cosmos-sdk/baseapp.BaseApp.DeliverTx,github.com/cosmos/cosmos-sdk/baseapp.BaseApp.BeginBlock,github.com/cosmos/cosmos-sdk/baseapp.BaseApp.EndBlock,github.com/cosmos/cosmos-sdk/baseapp.BaseApp.Commit'
+          pull_request_url: "${{ github.server_url }}/${{ github.repository }}/pull/${{ github.event.pull_request.number }}.patch"