Fix eta-expansion warnings

[xuwei-k]

https://docs.scala-lang.org/scala3/book/fun-eta-expansion.html

[warn] -- Warning: /home/runner/work/io/io/io/src/test/scala/sbt/io/FileUtilitiesSpecification.scala:21:61 
[warn] 21 |  property("Round trip string") = forAll(writeAndCheckString _)
[warn]    |                                         ^^^^^^^^^^^^^^^^^^^^^
[warn]    |The syntax `<function> _` is no longer supported;
[warn]    |you can simply leave out the trailing ` _`
[warn]    |This construct can be rewritten automatically under -rewrite -source 3.4-migration.
[warn] -- Warning: /home/runner/work/io/io/io/src/test/scala/sbt/io/FileUtilitiesSpecification.scala:22:59 
[warn] 22 |  property("Round trip bytes") = forAll(writeAndCheckBytes _)
[warn]    |                                        ^^^^^^^^^^^^^^^^^^^^
[warn]    |The syntax `<function> _` is no longer supported;
[warn]    |you can simply leave out the trailing ` _`
[warn]    |This construct can be rewritten automatically under -rewrite -source 3.4-migration.