Upgrade to yarn 4

Author: wpears

.github/workflows/build-artifact.yml

@@ -21,7 +21,7 @@ jobs:
             node-version: '20.x'
 
       - name: Install dependencies
-        run: yarn
+        run: yarn install --immutable --immutable-cache
 
       - name: Build frontend
         run: yarn run build

.github/workflows/frontend.yml

@@ -7,17 +7,22 @@ on:
 jobs:
   frontend:
     runs-on: ubuntu-latest
+    env:
+      YARN_ENABLE_NETWORK: 'false'
 
     steps:
       - uses: actions/checkout@v4
 
+      - name: Enable Corepack
+        run: corepack enable
+
       - name: Set up Node
         uses: actions/setup-node@v4
         with:
             node-version: '20.x'
 
       - name: Install dependencies
-        run: yarn
+        run: yarn install --immutable --immutable-cache
 
       - name: Test Javascript
         run: yarn run test

.github/workflows/functional-tests.yml

@@ -43,6 +43,9 @@ jobs:
     steps:
     - uses: actions/checkout@v4
 
+    - name: Enable Corepack
+      run: corepack enable
+
     - name: Set up Node
       uses: actions/setup-node@v4
       with:

.gitignore

@@ -28,6 +28,7 @@ cfgov/static_built/*
 !cfgov/agreements/tests/UTF_agreements.zip
 !cfgov/legacy/static/foia/quarterly/*.zip
 !cfgov/paying_for_college/data_sources/ipeds/test.txt.zip
+!npm-packages-offline-cache/*.zip
 
 # Desired minified CSS #
 ########################