Fix old varargs splice syntax

[xuwei-k]

https://docs.scala-lang.org/scala3/reference/changed-features/vararg-splices.html

[warn] -- Warning: /home/runner/work/io/io/io/src/main/scala/sbt/io/NameFilter.scala:141:90 
[warn] 141 |    case that: ExtensionFilter => new ExtensionFilter(this.extensions ++ that.extensions: _*)
[warn]     |                                                                                          ^
[warn]     |The syntax `x: _*` is no longer supported for vararg splices; use `x*` instead
[warn]     |This construct can be rewritten automatically under -rewrite -source 3.4-migration.
[warn] -- Warning: /home/runner/work/io/io/io/src/main/scala/sbt/io/NameFilter.scala:147:97 
[warn] 147 |    case that: ExtensionFilter => new ExtensionFilter(this.extensions intersect that.extensions: _*)
[warn]     |                                                                                                 ^
[warn]     |The syntax `x: _*` is no longer supported for vararg splices; use `x*` instead
[warn]     |This construct can be rewritten automatically under -rewrite -source 3.4-migration.
[warn] -- Warning: /home/runner/work/io/io/io/src/main/scala/sbt/io/NameFilter.scala:153:92 
[warn] 153 |    case that: ExtensionFilter => new ExtensionFilter(this.extensions diff that.extensions: _*)
[warn]     |                                                                                            ^
[warn]     |The syntax `x: _*` is no longer supported for vararg splices; use `x*` instead
[warn]     |This construct can be rewritten automatically under -rewrite -source 3.4-migration.
[warn] -- Warning: /home/runner/work/io/io/io/src/main/scala/sbt/io/NameFilter.scala:159:90 
[warn] 159 |    case that: ExtensionFilter => new ExtensionFilter(this.extensions ++ that.extensions: _*)
[warn]     |                                                                                          ^
[warn]     |The syntax `x: _*` is no longer supported for vararg splices; use `x*` instead
[warn]     |This construct can be rewritten automatically under -rewrite -source 3.4-migration.
[warn] -- Warning: /home/runner/work/io/io/io/src/main/scala/sbt/io/NameFilter.scala:165:97 
[warn] 165 |    case that: ExtensionFilter => new ExtensionFilter(this.extensions intersect that.extensions: _*)
[warn]     |                                                                                                 ^
[warn]     |The syntax `x: _*` is no longer supported for vararg splices; use `x*` instead
[warn]     |This construct can be rewritten automatically under -rewrite -source 3.4-migration.
[warn] -- Warning: /home/runner/work/io/io/io/src/main/scala/sbt/io/NameFilter.scala:171:92 
[warn] 171 |    case that: ExtensionFilter => new ExtensionFilter(this.extensions diff that.extensions: _*)
[warn]     |                                                                                            ^
[warn]     |The syntax `x: _*` is no longer supported for vararg splices; use `x*` instead
[warn]     |This construct can be rewritten automatically under -rewrite -source 3.4-migration.

[eed3si9n]

Thanks!