chore(workflows): update yarn install command to use --immutable flag for consistency in dependency management

Author: antony-lambdacurry

.github/workflows/github-pages.yml

@@ -41,7 +41,7 @@ jobs:
         run: corepack enable
 
       - name: Install dependencies
-        run: yarn install
+        run: yarn install --immutable
 
       - name: Build Storybook
         run: yarn build-storybook

.github/workflows/pr-preview.yml

@@ -40,7 +40,7 @@ jobs:
         run: corepack enable
 
       - name: Install dependencies
-        run: yarn install
+        run: yarn install --immutable
 
       - name: Build Storybook
         run: yarn build-storybook