Update CI to facilitate t-network/solidity-contracts dependency

The `@threshold-network/solidity-contract` dependency was added some time ago to
the `coverage-pools` project, but we haven't updated the `NPM` job accordingly.
We do it in this commit. We will update `Solidity` workflow in a separate PR.

Author: michalinacienciala

.github/workflows/npm.yml

@@ -37,7 +37,8 @@ jobs:
         run: |
           yarn upgrade --exact \
             @keep-network/keep-core \
-            @keep-network/tbtc
+            @keep-network/tbtc \
+            @threshold-network/solidity-contracts
 
       # Deploy contracts to a local network to generate deployment artifacts that
       # are required by dashboard compilation.