Sign Scala 3 nightlies

[Gedochao]

Compiler version

3.8.0-RC1-bin-20250916-eb1bb73-NIGHTLY

The bug

It seems we don't sign nightlies with .sha1 files

[error]   checksum format error: ~/Library/Caches/Coursier/v1/https/repo.scala-lang.org/ui/native/maven-nightlies/org/scala-lang/scala3-library_3/3.8.0-RC1-bin-20250916-eb1bb73-NIGHTLY/scala3-library_3-3.8.0-RC1-bin-20250916-eb1bb73-NIGHTLY.pom.sha1
[error]         at lmcoursier.CoursierDependencyResolution.unresolvedWarningOrThrow(CoursierDependencyResolution.scala:347)
[error]         at lmcoursier.CoursierDependencyResolution.$anonfun$update$39(CoursierDependencyResolution.scala:316)
[error]         at scala.util.Either$LeftProjection.map(Either.scala:573)
[error]         at lmcoursier.CoursierDependencyResolution.update(CoursierDependencyResolution.scala:316)
[error]         at sbt.librarymanagement.DependencyResolution.update(DependencyResolution.scala:60)
[error]         at sbt.internal.LibraryManagement$.resolve$1(LibraryManagement.scala:60)
[error]         at sbt.internal.LibraryManagement$.$anonfun$cachedUpdate$12(LibraryManagement.scala:142)
[error]         at sbt.util.Tracked$.$anonfun$lastOutput$1(Tracked.scala:74)
[error]         at sbt.internal.LibraryManagement$.$anonfun$cachedUpdate$11(LibraryManagement.scala:144)
[error]         at sbt.internal.LibraryManagement$.$anonfun$cachedUpdate$11$adapted(LibraryManagement.scala:131)
[error]         at sbt.util.Tracked$.$anonfun$inputChangedW$1(Tracked.scala:220)
[error]         at sbt.internal.LibraryManagement$.cachedUpdate(LibraryManagement.scala:169)
[error]         at sbt.Classpaths$.$anonfun$updateTask0$1(Defaults.scala:3993)
[error]         at scala.Function1.$anonfun$compose$1(Function1.scala:49)
[error]         at sbt.internal.util.$tilde$greater.$anonfun$$u2219$1(TypeFunctions.scala:63)
[error]         at sbt.std.Transform$$anon$4.work(Transform.scala:69)
[error]         at sbt.Execute.$anonfun$submit$2(Execute.scala:283)
[error]         at sbt.internal.util.ErrorHandling$.wideConvert(ErrorHandling.scala:24)
[error]         at sbt.Execute.work(Execute.scala:292)
[error]         at sbt.Execute.$anonfun$submit$1(Execute.scala:283)
[error]         at sbt.ConcurrentRestrictions$$anon$4.$anonfun$submitValid$1(ConcurrentRestrictions.scala:265)
[error]         at sbt.CompletionService$$anon$2.call(CompletionService.scala:65)
[error]         at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:317)
[error]         at java.base/java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:572)
[error]         at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:317)
[error]         at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1144)
[error]         at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:642)
[error]         at java.base/java.lang.Thread.run(Thread.java:1575)

Expectation

Nightlies should be signed, just like any other Scala 3 release.

[hamzaremmal]

As I mentioned to @Gedochao offline, this was down in my TODOs as it was never blocking things, but I'll bump it up as it is an easy task.