Make allowed version of freemarker explicit

The freemarker docs state, that it is not allowed to use Config#getVersion()
directly, to specify the version, that we think we are compatible with.

Therefore, let us specify the current version and update it, as we update
the dependency or the templates.

src/core/src/main/java/org/apache/jmeter/report/dashboard/HtmlTemplateExporter.java

@@ -442,7 +442,7 @@ public void export(SampleContext context, File file,
         addToContext(DATA_CTX_OVERALL_FILTER, configuration.getSampleFilter(), dataContext);
 
         // Walk template directory to copy files and process templated ones
-        Configuration templateCfg = new Configuration(Configuration.getVersion());
+        Configuration templateCfg = new Configuration(Configuration.VERSION_2_3_30);
         try {
             templateCfg.setDirectoryForTemplateLoading(templateDirectory);
             templateCfg.setTemplateExceptionHandler(TemplateExceptionHandler.RETHROW_HANDLER);

src/core/src/main/java/org/apache/jmeter/util/TemplateUtil.java

@@ -43,7 +43,7 @@ private TemplateUtil() {
     }
 
     private static Configuration init() {
-        Configuration templateConfiguration = new Configuration(Configuration.getVersion());
+        Configuration templateConfiguration = new Configuration(Configuration.VERSION_2_3_30);
         templateConfiguration.setDefaultEncoding(StandardCharsets.UTF_8.name());
         templateConfiguration.setInterpolationSyntax(Configuration.SQUARE_BRACKET_INTERPOLATION_SYNTAX);
         templateConfiguration.setTemplateExceptionHandler(TemplateExceptionHandler.RETHROW_HANDLER);