Update navconfig.json (MystenLabs#9210)

## Description 

Describe the changes or additions included in this PR.

## Test Plan 

How did you test the new or updated feature?

---
If your changes are not user-facing and not a breaking change, you can
skip the following section. Otherwise, please indicate what changed, and
then add to the Release Notes section as highlighted during the release
process.

### Type of Change (Check all that apply)

- [ ] user-visible impact
- [ ] breaking change for a client SDKs
- [ ] breaking change for FNs (FN binary must upgrade)
- [ ] breaking change for validators or node operators (must upgrade
binaries)
- [ ] breaking change for on-chain data layout
- [ ] necessitate either a data wipe or data migration

### Release notes

doc/src/navconfig.json

@@ -200,7 +200,7 @@
 					},
 					{
 						"label": "Sui Validator node",
-						"fileName": "build/validator-node.md"
+						"fileName": "build/validator-node"
 					},
 					{
 						"label": "Event Query and Subscription",