Switch to pnpm

TBH I don't really care between pnpm and yarn, but the new runner image only has pnpm so here I go

.forgejo/workflows/build.yaml

@@ -13,13 +13,13 @@ jobs:
       - name: Set up Node
         uses: actions/setup-node@v4
       - name: Install dependencies
-        run: yarn install
+        run: pnpm install
       - name: Check code formatting
-        run: yarn lint:prettier
+        run: pnpm lint:prettier
       - name: Check code quality
-        run: yarn lint:eslint
+        run: pnpm lint:eslint
       - name: Check types
-        run: yarn lint:tsc
+        run: pnpm lint:tsc
 
   build:
     name: Build
@@ -30,9 +30,9 @@ jobs:
       - name: Set up Node
         uses: actions/setup-node@v4
       - name: Install dependencies
-        run: yarn install
+        run: pnpm install
       - name: Build
-        run: yarn build
+        run: pnpm build
       - name: Save build
         uses: forgejo/upload-artifact@v4
         with: