go.mod: bump cockroachdb/swiss for Go 1.26 support

[chenrui333]

go.mod: bump cockroachdb/swiss for Go 1.26 support

• go 1.26.0, go@1.25 1.25.7 (new formula) Homebrew/homebrew-core#258912
• Enable Go 1.26 support cockroachdb/swiss#50

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[gammazero]

Handled in dependency update PR #190