Bump isabelle-theory-build action to v9

Author: cplaursen

.github/workflows/build_2025.yml

@@ -5,7 +5,7 @@ jobs:
     name: Build Theory
     steps:
       - uses: actions/checkout@v3
-      - uses: lexbailey/isabelle-theory-build-github-action@v8
+      - uses: lexbailey/isabelle-theory-build-github-action@v9
         with:
           isabelle-url: 'https://github.com/seL4/isabelle/archive/refs/tags/Isabelle2025.tar.gz'
           report_url: 'https://isabelle-utp-ci-dashboard.link/submit_job_log'