Potential fix for code scanning alert no. 3: Workflow does not contain permissions

Co-authored-by: Copilot Autofix powered by AI <62310815+github-advanced-security[bot]@users.noreply.github.com>

Author: korewaChino

.github/workflows/build_riscv_rva23.yml

@@ -4,6 +4,10 @@ on:
   push:
   pull_request:
 
+permissions:
+  contents: read
+  actions: read
+
 env:
   CARGO_TERM_COLOR: always