ci(npm-random-beacon): pin @threshold-network/solidity-contracts to 1.2.1

The `development` dist-tag was bumped to 1.3.0-dev.16, which refactored
`TokenStaking` so `approveApplication` is no longer exposed by the
deployed ABI. The deploy script
`solidity/random-beacon/deploy/05_approve_random_beacon_in_token_staking.ts`
calls that function and fails the CI publish step.

Pin to the last compatible version (1.2.1) so publishes succeed while
the deploy scripts and Go ABI bindings are migrated to the 1.3 API in
a separate PR.

Author: piotr-roslaniec

.github/workflows/npm-random-beacon.yml

@@ -34,10 +34,15 @@ jobs:
           cache-dependency-path: solidity/random-beacon/yarn.lock
 
       - name: Resolve latest contracts
+        # `@threshold-network/solidity-contracts` is pinned to 1.2.1 because
+        # the `development` dist-tag was bumped to 1.3.0-dev, which refactored
+        # `TokenStaking` and removed `approveApplication` (called by
+        # `deploy/05_approve_random_beacon_in_token_staking.ts`). Unpin once
+        # the deploy scripts and Go ABI bindings are migrated to the 1.3 API.
         run: |
           yarn upgrade --exact \
             @keep-network/sortition-pools \
-            @threshold-network/solidity-contracts
+            @threshold-network/solidity-contracts@1.2.1
 
       # Deploy contracts to a local network to generate deployment artifacts that
       # are required by dashboard and client compilation.