Upgrade to explicit keep-core version when publishing on testnet

We provide explicit version of the `keep-core` package, because using
`development` tag results in `expected manifest` error - probably caused by bug
in Yarn: yarnpkg/yarn#4731. We don't plan to publish new
`@keep-network/keep-core` anytime soon, so this should be an acceptable
workaround.

.github/workflows/dashboard-ci.yml

@@ -73,7 +73,7 @@ jobs:
         run: |
           yarn upgrade \
             @threshold-network/solidity-contracts \
-            @keep-network/keep-core \
+            @keep-network/keep-core@1.8.1-goerli.0 \
             @keep-network/keep-ecdsa \
             @keep-network/tbtc \
             @keep-network/coverage-pools \