fix: use raw=True (capitalized) in read_file tool description

Agent-Logs-Url: https://github.com/Serverless-Devs/agentrun-sdk-python/sessions/410c37c7-b485-46a3-806d-026c8d397150

Co-authored-by: OhYee <13498329+OhYee@users.noreply.github.com>

Author: Copilot

agentrun/integration/builtin/sandbox.py

@@ -389,7 +389,7 @@ def inner(sb: Sandbox):
         description=(
             "Read the content of a file at the specified path in the sandbox."
             " By default returns the file content encoded as a base64 string."
-            " Set raw=true to get the plain text content instead."
+            " Set raw=True to get the plain text content instead."
             " Suitable for reading code files, configs, logs, binary files,"
             " etc."
         ),