chore(deps): update ubuntu docker tag to v26 (#106)

This PR contains the following updates:

| Package | Type | Update | Change |
|---|---|---|---|
| ubuntu | final | major | `24.04` → `26.04` |

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Dockerfile.test

@@ -1,5 +1,5 @@
 # Test environment for crabcode
-FROM ubuntu:24.04
+FROM ubuntu:26.04
 
 # Install dependencies
 RUN apt-get update && apt-get install -y \