Add job pinned to tendermint-go v0.33.5

Closes informalsystems#304

Also rename test-integration-ignored to test-integration-latest.

The latest integration tracks whether we're maintaining parity with the
latest development version of tendermint-go, while the stable
integration ensures we avoid regressions.

.github/workflows/rust.yml

@@ -61,11 +61,34 @@ jobs:
           command: test
           args: --all-features --no-fail-fast
 
-  test-integration-ignored:
+  # TODO(shonfeder): remove duplication once GitHub address
+  #  - https://github.community/t/support-for-yaml-anchors/16128/15, or
+  #  - https://github.community/t/reusing-sharing-inheriting-steps-between-jobs-declarations/16851/13
+  test-integration-stable:
     runs-on: ubuntu-latest
     services:
       tendermint:
-        image: tendermint/tendermint
+        image: tendermint/tendermint:v0.33.5
+        ports:
+          - 26656:26656
+          - 26657:26657
+          - 26660:26660
+    steps:
+      - uses: actions/checkout@v2
+      - uses: actions-rs/toolchain@v1
+        with:
+          toolchain: stable
+          override: true
+      - uses: actions-rs/cargo@v1
+        with:
+          command: test
+          args: -p tendermint --test integration --no-fail-fast -- --ignored
+
+  test-integration-latest:
+    runs-on: ubuntu-latest
+    services:
+      tendermint:
+        image: tendermint/tendermint:latest
         ports:
           - 26656:26656
           - 26657:26657