chore: bump nightly version to 0.16.0-nightly-20250728 (#1979)

Co-authored-by: nicecui <[email protected]>

Author: github-actions[bot]

variables/variables-nightly.ts

@@ -1,5 +1,5 @@
 export const variables = {
-  greptimedbVersion: 'v0.16.0-nightly-20250714',
+  greptimedbVersion: 'v0.16.0-nightly-20250728',
   prometheusVersion: 'v2.52.0',
   nodeExporterVersion: 'v1.8.0',
   goSdkVersion: 'v0.6.2',