Fix build (babel helper-compilation-targets workaround)

This is a bug in babel: babel/babel#11216
It is closed but points to an issue in node: nodejs/node#32107
The issue in node is closed as not an issue, so it seems as though babel needs to fix.

Also, check that build works in PRs.

.github/workflows/npm-publish.yaml

@@ -14,7 +14,7 @@ jobs:
       - uses: actions/checkout@v1
       - uses: actions/setup-node@v1
         with:
-          node-version: 12
+          node-version: 12.16.1 # workaround https://github.com/babel/babel/issues/11216
           registry-url: https://registry.npmjs.org/
       - run: yarn
       - run: yarn build

.github/workflows/tests.yaml

@@ -9,6 +9,7 @@ jobs:
       - uses: actions/checkout@v1
       - uses: actions/setup-node@v1
         with:
-          node-version: 12
+          node-version: 12.16.1 # workaround https://github.com/babel/babel/issues/11216
       - run: yarn
       - run: yarn test
+      - run: yarn build