fix: rename the last ComposableCoW-cased test filename

[mfw78]

test/ComposableCoW.t.sol was missed by the rename in #44, leaving it as the only remaining ComposableCoW-cased filename in the tree that is not a deliberate exception.

The pattern used in #44 matched test/ComposableCoW.*.t.sol, which requires a middle segment (.base., .twap., ...). The one file without one never matched. Its contents were renamed correctly, so a search over file bodies came back clean and the miss went unnoticed.

Filename only, zero content change: the contract inside is already ComposableCowTest, nothing references the path, and .gas-snapshot keys off contract names rather than filenames.

Remaining ComposableCoW-cased paths after this are both deliberate: audits/gnosis-ComposableCoWMayJul2023.pdf (published artefact) and broadcast/StandardJsonInput/ComposableCoW.json (historical deployment record).

How to test

git ls-tree -r --name-only HEAD | rg 'ComposableCoW'

Returns only the two intentional exceptions above.

Part of #1.

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