Use JDK 11 in the CI and bump the JVM toolchain version to 11

Bytecode compatibility shouldn't be an issue in dependent Java 8 projects because the project only uses Kotlin/JS.

The message from the CI run:

```text
> Task :compose-html-material-gradle-plugins-legacy:extractPrecompiledScriptPluginPlugins
e: java.lang.UnsupportedClassVersionError: androidx/compose/compiler/plugins/kotlin/ComposePluginRegistrar has been compiled by a more recent version of the Java Runtime (class file version 55.0), this version of the Java Runtime only recognizes class file versions up to 52.0
	at java.lang.ClassLoader.defineClass1(Native Method)
	at java.lang.ClassLoader.defineClass(ClassLoader.java:757)
```

.github/workflows/kotlin-multiplatform-ci.yml

@@ -15,11 +15,11 @@ jobs:
 
     steps:
       - uses: actions/checkout@v4
-      - name: Set up JDK 8
+      - name: Set up JDK 11
         uses: actions/setup-java@v4
         with:
-          java-version: '8'
-          distribution: 'zulu'
+          java-version: '11'
+          distribution: 'temurin'
 
       - name: Setup Gradle
         uses: gradle/actions/setup-gradle@v4
@@ -35,11 +35,11 @@ jobs:
 
     steps:
       - uses: actions/checkout@v4
-      - name: Set up JDK 8
+      - name: Set up JDK 11
         uses: actions/setup-java@v4
         with:
-          java-version: '8'
-          distribution: 'zulu'
+          java-version: '11'
+          distribution: 'temurin'
 
       - name: Generate and submit dependency graph
         uses: gradle/actions/dependency-submission@v4