add corepack: true field in all github workflows to prevent yarn error

Author: emhgit

.github/workflows/build-tests.yml

@@ -16,6 +16,7 @@ jobs:
         uses: actions/setup-node@v4
         with:
           node-version: 20.x
+          corepack: true
       - uses: dart-lang/setup-dart@v1
 
       - run: yarn add serve@14.2.4

.github/workflows/prettier.yml

@@ -12,6 +12,8 @@ jobs:
     steps:
       - uses: actions/checkout@v4
       - uses: actions/setup-node@v4
+        with:
+          corepack: true
       - run: |
           yarn
           yarn prettier . --write

.github/workflows/test.yml

@@ -23,6 +23,7 @@ jobs:
         uses: actions/setup-node@v4
         with:
           node-version: 20.x
+          corepack: true
       - name: Cache node modules
         uses: actions/cache@v4
         id: cache-node-modules
@@ -52,9 +53,10 @@ jobs:
     steps:
       - uses: actions/checkout@v4
       - name: Use Node.js 20.x
-        uses: actions/setup-node@v1
+        uses: actions/setup-node@v4
         with:
           node-version: 20.x
+          corepack: true
 
       - name: Cache node modules
         uses: actions/cache@v4

.github/workflows/update-usaco.yml

@@ -14,6 +14,7 @@ jobs:
         uses: actions/setup-node@v4
         with:
           node-version: 20.x
+          corepack: true
       - name: Checkout usaco-problems
         uses: actions/checkout@v4
         with: