Migrate scala/* repos to GitHub Actions

[SethTisue]

we'll still have a one-concurrent-job plan on Travis-CI, so we can still do Scala releases and run a few other jobs

https://app.travis-ci.com/github/scala shows which repos are active

• sbt-scala-module
  • replace Travis-CI with GitHub Actions sbt-scala-module#139
  • modules will use GitHub Actions, not Travis-CI sbt-scala-module#140
  • https://github.com/scala/sbt-scala-module/releases/tag/v3.0.0
• modules:
  • scala-async: Update sbt-scala-module to 2.4.0 scala-async#274, replace Travis-CI with GitHub Actions scala-async#278, Publish version 1.0.1 scala-async#276
  • scala-parser-combinators: Update sbt-scala-module to 2.4.0 scala-parser-combinators#415, in with GitHub Actions, out with Travis-CI scala-parser-combinators#416, Release version 2.1.0 scala-parser-combinators#418
  • scala-parallel-collections: add GitHub Actions, drop Travis-CI scala-parallel-collections#193, Release version 1.0.4 scala-parallel-collections#195
  • scala-java8-compat: in with GitHub Actions, out with Travis-CI scala-java8-compat#242, Release version 1.0.1 scala-java8-compat#245
  • scala-xml: in with GitHub Actions, out with Travis-CI scala-xml#564
  • scala-swing: replace Travis-CI with GitHub Actions scala-swing#157
  • scala-collection-contrib: Update sbt-scala-module to 2.4.0 scala-collection-contrib#151, replace Travis-CI with GitHub Actions scala-collection-contrib#152
  • scala-library-next: replace Travis-CI with GitHub Actions scala-library-next#98
  • scala-collection-compat: replace Travis-CI with GitHub Actions scala-collection-compat#485 (abandoned), upgrade to sbt-scala-module 3.0.0 scala-collection-compat#486, replace Travis-CI with GitHub Actions scala-collection-compat#487, add publishing to GitHub Actions scala-collection-compat#488
• websites:
  • scala.epfl.ch: Seb says he'll find somebody (Switch from Travis-CI to GitHub Actions, please? scala.epfl.ch#194)
  • scala-lang: Migrate to Github Actions scala-lang#1276
  • docs.scala-lang: switch from Travis-CI to GitHub Actions docs.scala-lang#2176
• other:
  • scala-rewrites: Switch from Travis-CI to GitHub Actions lightbend-labs/scala-rewrites#125
• scala-dist, scala-dist-smoketest, scabot, scala-asm:
  • can we just leave these alone? maybe rotate their secrets?
• nanotest-strawman: modernize GitHub Actions config somewhat eed3si9n/verify#160
• giter8 templates

[SethTisue]

separate ticket on CLA checking: #792

[SethTisue]

Not all checkboxes are checked, but I think we've done enough. We can do any other migrations as needed.