CI, build.gradle: java updated to version 21 (#28)

* CI, build.gradle: java updated to version 21

* binexport: updated submodule to be able to compile with JDK 21

* README.md: changed JDK 17 to JDK 21

.github/workflows/main.yml

@@ -32,7 +32,7 @@ jobs:
       uses: actions/setup-java@v4
       with:
         distribution: 'temurin'
-        java-version: '17'
+        java-version: '21'
 
     - name: Install Gradle
       uses: gradle/actions/setup-gradle@v3

Readme.md

@@ -105,7 +105,7 @@ Select the other file from the tree and click OK.
 Requirements:
 
 * Ghidra installation (https://ghidra-sre.org) or compiled from source
-* Some jdk. There might be certain restrictions depending on how your Ghidra was built and what other plugins you're using. I recommend using [Temurin 17 LTS](https://adoptium.net/temurin/releases/?version=17), as this currently seems to work with both BinExport and BinDiffHelper. 
+* Some jdk. There might be certain restrictions depending on how your Ghidra was built and what other plugins you're using. I recommend using [Temurin 21 LTS](https://adoptium.net/temurin/releases/?version=21), as this currently seems to work with both BinExport and BinDiffHelper. 
 * gradle (tested with 7.5, 8.10)
 
 ### Clone the repository

build.gradle

@@ -3,7 +3,7 @@ apply plugin: 'eclipse'
 
 java {
     toolchain {
-        languageVersion = JavaLanguageVersion.of(17)
+        languageVersion = JavaLanguageVersion.of(21)
     }
 }