Change lambda parameter to pass by value

[alexeagle]

clang-tidy will flag as an unnecessary copy (performance-unnecessary-value-param)

[aspect-workflows]

Test

All tests were cache hits

26 tests (100.0%) were fully cached saving 44s.

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Lint

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2 issues require fixes
1 issues can be fixed automatically

💡 Auto-fix linting errors with:

bazel lint //speller/main:build-dictionary --fix

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Buildifier      Format      Gazelle

[aspect-workflows]

ClangTidy provided a suggestion

Suggested change

	[&](string word) { engine.AddEntry(word); });
	[&](const string& word) { engine.AddEntry(word); });