ci: install yarn for actions on forgejo

Summary:

The forgejo action use act under the hood. The default image does not have yarn
installed so, this is installing it.

Test Plan:

CI

.github/workflows/ci.yml

@@ -18,6 +18,9 @@ jobs:
           node-version: 18
           cache: yarn
 
+      - name: Install yarn
+        run: npm i -g yarn
+
       - name: Install dependencies
         run: yarn install
 
@@ -44,6 +47,9 @@ jobs:
           node-version: ${{ matrix.node-version }}
           cache: yarn
 
+      - name: Install yarn
+        run: npm i -g yarn
+
       - name: Install dependencies
         run: yarn install