fix: do not delete test data directory (ethereum-optimism#11869)

Our "just clean" command was deleting the entirety of .testdata
which gets in several scripts now. We don't actually want to
delete the entirety of .testdata, we want to delete anything
inside of it (except for the gitkeep file).

Author: smartcontracts

packages/contracts-bedrock/justfile

@@ -111,8 +111,11 @@ validate-spacers-no-build:
 
 validate-spacers: build validate-spacers-no-build
 
+# Cleans build artifacts and deployments.
+# Removes everything inside of .testdata (except the .gitkeep file).
 clean:
-  rm -rf ./artifacts ./forge-artifacts ./cache ./scripts/go-ffi/go-ffi ./.testdata ./deployments/hardhat/*
+  rm -rf ./artifacts ./forge-artifacts ./cache ./scripts/go-ffi/go-ffi ./deployments/hardhat/*
+  find ./.testdata -mindepth 1 -not -name '.gitkeep' -delete
 
 pre-pr-no-build: gas-snapshot-no-build snapshots-no-build semver-lock autogen-invariant-docs lint