chore: update .env.example by replacing Bohrium keys with Materials keys

Author: Rasic2

.env.example

@@ -6,13 +6,8 @@ AZURE_API_KEY=xxx
 # DEEPSEEK_API_KEY=xxxx
 
 OPIK_PROJECT_NAME=test
-# test (https://www.test.bohrium.com/)
-BOHRIUM_ACCESS_KEY=xxxx
-BOHRIUM_PROJECT_ID=xxxx
-
-# prod (https://www.bohrium.com/)
-# BOHRIUM_ACCESS_KEY=xxxx
-# BOHRIUM_PROJECT_ID=xxxx
+MATERIALS_ACCESS_KEY=xxxx
+MATERIALS_PROJECT_ID=xxxx
 
 OPENAI_API_KEY=sk-XX
 GPT_CHAT_MODEL=gpt-5-chat