Automatic upgrade of CBMC from 6.10.0 to 6.11.0

[github-actions]

Upgrade CBMC to its latest release.

[feliperodri]

Blocked on diffblue/homebrew-cbmc#36. The only real CI failure here is macOS — the install step runs brew install diffblue/cbmc/cbmc@6.11.0, but that formula doesn't exist in the tap yet (the Linux regression/verify-std jobs just got cancelled by fail-fast, and perf/llbc-regression already ran green on 6.11.0). The tap's automation already opened diffblue/homebrew-cbmc#36 with the formula, but it needs a maintainer to approve its pending brew test-bot run and add the pr-pull label to publish. Once that's merged, macOS CI here should pass. @tautschnig could you take a look?