Keep group pane size when resizing window (#6180) (#6423)

* Keep group pane size when resizing window (#6180)

* add changelog for fixing issue 6180

Co-authored-by: Hollyqqqqq <11712639@mail.sustech.edu.cn>
Co-authored-by: Tobias Diez <tobiasdiez@gmx.de>

CHANGELOG.md

@@ -46,6 +46,7 @@ Note that this project **does not** adhere to [Semantic Versioning](http://semve
 - We fixed an issue where opening a library from the recent libraries menu was not possible. [#5939](https://github.com/JabRef/jabref/issues/5939)
 - We fixed an issue with inconsistent capitalization of file extensions when downloading files. [#6115](https://github.com/JabRef/jabref/issues/6115)
 - We fixed the display of language and encoding in the preferences dialog. [#6130](https://github.com/JabRef/jabref/pull/6130)
+- We fixed the issue that groups panel does not keep size when resizing window. [#6180](https://github.com/JabRef/jabref/issues/6180)
 - We fixed an error that sometimes occurred when using the context menu. [#6085](https://github.com/JabRef/jabref/issues/6085)
 - We fixed an issue where search full-text documents downloaded files with same name, overwriting existing files. [#6174](https://github.com/JabRef/jabref/pull/6174)
 - We fixed an issue when importing into current library an erroneous message "import cancelled" is displayed even though import is successful. [#6266](https://github.com/JabRef/jabref/issues/6266)
@@ -60,7 +61,6 @@ Note that this project **does not** adhere to [Semantic Versioning](http://semve
 - We fixed an issue where the Preferences entry preview will be unexpected modified leads to Value too long exception [#6198](https://github.com/JabRef/jabref/issues/6198)
 - We fixed an issue where custom jstyles for Open/LibreOffice would only be valid if a layout line for the entry type `default` was at the end of the layout section [#6303](https://github.com/JabRef/jabref/issues/6303)
 - We fixed an issue where long directory names created from patterns could create an exception. [#3915](https://github.com/JabRef/jabref/issues/3915)
-
 - We fixed an issue where sort on numeric cases was broken. [#6349](https://github.com/JabRef/jabref/issues/6349)
 - We fixed an issue where year and month fields were not cleared when converting to biblatex [#6224](https://github.com/JabRef/jabref/issues/6224)
 - We fixed an issue where an "Not on FX thread" exception occured when saving on linux [#6453](https://github.com/JabRef/jabref/issues/6453)

src/main/java/org/jabref/gui/JabRefFrame.java

@@ -457,6 +457,7 @@ private void initLayout() {
         setTop(head);
 
         splitPane.getItems().addAll(sidePane, tabbedPane);
+        splitPane.setResizableWithParent(sidePane, false);
 
         // We need to wait with setting the divider since it gets reset a few times during the initial set-up
         mainStage.showingProperty().addListener(new ChangeListener<>() {