ctxscope v1.0.2 — stop forcing a linter upgrade on importers

The golangci-lint tool pin was v2.12.2. A tool directive is still a require and
Go takes the maximum across the module graph, so importing ctxscope raised every
consumer's linter and lit up findings in code they had not touched.

Pinned to v2.4.0 to match ctxerrors. Importing this module can no longer move
anyone's linter. No library code changed.