Update library used to generate Excel files (#125)

Fixes #94
Fixes #93

## How to test
1. Log in as the default admin
2. Go to "Project management / Projects"
3. Click "Download as Excel" under the table
4. See that it's still a valid Excel-file

Reviewed-on: #125
Reviewed-by: Nico Athanassiadis <nico@dsv.su.se>
Co-authored-by: Andreas Svanberg <andreass@dsv.su.se>
Co-committed-by: Andreas Svanberg <andreass@dsv.su.se>

pom.xml

@@ -26,7 +26,7 @@
         <wicket.version>10.4.0</wicket.version>
         <jakarta.persistence-api.version>3.1.0</jakarta.persistence-api.version>
         <querydsl.version>5.0.0</querydsl.version>
-        <poi.version>5.2.5</poi.version>
+        <poi.version>5.4.0</poi.version>
 
         <!--
             When updating spring-boot check if the transitive dependency on json-smart has been