CI: Use pnpm rather than yarn with Hardhat

.circleci/config.yml

@@ -34,7 +34,10 @@ commands:
     steps:
       - run:
           name: Versions
-          command: npm version
+          command: |
+            npm version
+            yarn --version
+            pnpm version || >&2 echo "pnpm not installed"
 
   update-npm:
     steps:
@@ -99,7 +102,7 @@ commands:
         default: workspace/solc-js.tgz
       package-manager:
         type: enum
-        enum: ["npm", "yarn"]
+        enum: ["npm", "yarn", "pnpm"]
         default: npm
     steps:
       - run:
@@ -124,7 +127,7 @@ commands:
               jq --raw-output .version
             )
             cd "<<parameters.path>>"
-            if "<<parameters.package-manager>>" list --pattern solc | grep 'solc@' | grep -v "solc@${solc_version}"; then
+            if "<<parameters.package-manager>>" list solc | grep 'solc@' | grep -v "solc@${solc_version}"; then
               echo "Another version of solc-js is still present in the dependency tree."
               exit 1
             fi
@@ -136,11 +139,11 @@ commands:
       - install-dependencies:
           cache-id: hardhat
           path: hardhat
-          package-manager: yarn
-          dependency-file: yarn.lock
+          package-manager: pnpm
+          dependency-file: pnpm-lock.yaml
       - inject-solc-js-tarball:
           path: hardhat/
-          package-manager: yarn
+          package-manager: pnpm
 
   provision-truffle-with-packaged-solcjs:
     description: "Clones Truffle repository and configures it to use a local clone of solc-js."
@@ -247,17 +250,17 @@ jobs:
             hardhat_default_solc_version=$(jq --raw-output '.dependencies.solc' hardhat/packages/hardhat-core/package.json)
             mkdir hardhat-default-solc/
             pushd hardhat-default-solc/
-            npm install "solc@${hardhat_default_solc_version}"
+            pnpm install "solc@${hardhat_default_solc_version}"
             popd
             ln -sf ../../../hardhat-default-solc/node_modules/solc/soljson.js hardhat/node_modules/solc/soljson.js
       - run:
           name: Run hardhat-core test suite with its default solc binary
           command: |
             cd hardhat/packages/hardhat-core
-            # TODO: yarn build should not be needed to run these tests. Remove it.
+            # TODO: pnpm build should not be needed to run these tests. Remove it.
             # See https://github.com/NomicFoundation/hardhat/issues/2486 for details.
-            yarn build
-            yarn test
+            pnpm build
+            pnpm test
 
   hardhat-core-latest-solc:
     docker:
@@ -276,7 +279,7 @@ jobs:
             export HARDHAT_TESTS_SOLC_PATH HARDHAT_TESTS_SOLC_VERSION
 
             cd packages/hardhat-core/
-            yarn test
+            pnpm test
 
   hardhat-sample-project:
     docker: