Use FLINT 3.4

Author: oscarbenjamin

.github/workflows/buildwheel.yml

@@ -331,7 +331,7 @@ jobs:
 
   test_cython_api:
     name: Test experimental Cython API
-    runs-on: ubuntu-24.04
+    runs-on: ubuntu-26.04
     steps:
       - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
         with: