ci: install fern-api globally in workflows that invoke fern

The fern CLI isn't a workspace dependency, so `yarn install` doesn't put
it on PATH and `yarn fern-check` fails with `/bin/sh: 1: fern: not found`.
Install fern-api globally in fern-check and publish-docs before any step
that calls fern directly.

Author: Devon-White

.github/workflows/check.yml

@@ -21,6 +21,9 @@ jobs:
       - name: Install dependencies
         run: yarn install
 
+      - name: Install Fern CLI
+        run: npm install -g fern-api
+
       - name: Check API is valid
         run: yarn fern-check
         env:

.github/workflows/publish-docs.yml

@@ -21,6 +21,9 @@ jobs:
       - name: Install dependencies
         run: yarn install
 
+      - name: Install Fern CLI
+        run: npm install -g fern-api
+
       - name: Build TypeSpec specifications
         run: yarn build:specs