Normalize extendedJavaHome environment variable

The extendedJavaHome environment variable contains `.` symbols in the version. This causes the environment variable to be ignored by the action runner. It's best to replace those and other non standard symbols with and underscore.

For reference:
> Environment variable names used by the utilities in the Shell and Utilities volume of IEEE Std 1003.1-2001 consist solely of uppercase letters, digits, and the '_' (underscore) from the characters defined in Portable Character Set .

src/installer.ts

@@ -87,6 +87,7 @@ export async function getJava(
   }
 
   let extendedJavaHome = 'JAVA_HOME_' + version + '_' + arch;
+  extendedJavaHome = extendedJavaHome.toUpperCase().replace(/[^0-9A-Z_]/g, '_');
   core.exportVariable('JAVA_HOME', toolPath);
   core.exportVariable(extendedJavaHome, toolPath);
   core.addPath(path.join(toolPath, 'bin'));