fix: display the "contributing" section in the navbar (#2748)

The file that was previously referenced in the Antora configuration
didn't exist. Use the right one.


### Screenshots


![image](https://github.com/bonitasoft/bonita-doc/assets/27200110/aa25a8b9-bfa4-4a83-a33c-98417a546bcc)


### Notes

The new Antora versions now generate a warning when a nav entry cannot
be resolved. This is how the problem has been detected.
Detected in
bonitasoft/bonita-documentation-site#736 (comment)

antora.yml

@@ -38,4 +38,4 @@ nav:
   - modules/runtime/runtime-nav.adoc
   - modules/security/security-nav.adoc
   - modules/version-update/version-update-nav.adoc
-  - modules/ROOT/build-community-nav.adoc
+  - modules/contributing/contributing-nav.adoc