Release 3.1.5: remove debug println, drop worksheet leftover, modernize CI

- Remove stray println(child.value) from TreeNode.removeChild()
- Add regression test for removeChild() return value
- Delete leftover ExampleUnitTest.kt template test
- Remove Example.ws.kts worksheet and kotlin("script-runtime") from jvmMain
- Bump actions/checkout v2 -> v4 in CI workflows
- Update README install snippets to 3.1.5
- Bump version to 3.1.5

.github/workflows/publishRelease.yml

@@ -18,7 +18,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Check out code
-        uses: actions/checkout@v2
+        uses: actions/checkout@v4
       - name: Set up JDK 21
         uses: actions/setup-java@v4
         with:

.github/workflows/test.yml

@@ -11,7 +11,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Check out code
-        uses: actions/checkout@v2
+        uses: actions/checkout@v4
       - name: Set up JDK 21
         uses: actions/setup-java@v4
         with: