Don't show no-op regex-lint output. (#14656)
Don't show no-op regex-lint output. (#14656)

Other linters only display output if they acted on at least one file.
Previously, we would always show regex-lint output, even in the
no-op case of acting on no files. This change brings regex-lint
into line with the other linters.

[ci skip-rust]

[ci skip-build-wheels]

benjyw/pants,benjyw/pants,pantsbuild/pants,benjyw/pants,benjyw/pants,pantsbuild/pants,pantsbuild/pants,benjyw/pants,benjyw/pants,pantsbuild/pants,pantsbuild/pants,pantsbuild/pants,benjyw/pants,pantsbuild/pants