Keep test files meant for scripted tests within a template

[mkurz]

Fixes #394

To test this I ran sbt new sbt/sbt-autoplugin.g8. Like reported in #394 the src/sbt-test/sbt-foo-bar/simple/test was missing.

Now I did

1. To simulate this PR I added to the .gitignore file:

test
!**/sbt-test/**/test
!test/

1. created the file src/sbt-test/sbt-foo-bar/simple/test (the one that should not be ignored)
2. More testing by adding a sbt-test folder to the root dir containing various test files in various levels and a test file in the root folder and in a directory e.g scr/main/.

Now running:

$ git add .
$ git status 
On branch main
Changes to be committed:
  (use "git restore --staged <file>..." to unstage)
        modified:   .gitignore
        new file:   sbt-test/foo/bar/test
        new file:   sbt-test/foo/test
        new file:   sbt-test/test
        new file:   src/sbt-test/sbt-foo-bar/simple/test

It's exactly what I wanted to see. All test files containted within a sbt-test folder get added, no matter which level they are in and no matter at which level the sbt-test folder is. All other test files get ignored.

[eed3si9n]

Thanks!