fix: update Go toolchain to 1.24.6 to resolve GO-2025-3849 vulnerability (#2311)

Updates the Go toolchain version from `go1.24.4` to `go1.24.6` to
address the security vulnerability GO-2025-3849 in the standard
library's `database/sql` package.

## Vulnerability Details
- **ID**: GO-2025-3849
- **Package**: `database/sql` (standard library)
- **Issue**: Incorrect results returned from `Rows.Scan`
- **Affected version**: go1.24.4 and earlier
- **Fixed in**: go1.24.6

## Impact
The vulnerability affects the PostgreSQL indexer functionality in
celestia-core, specifically:
- `./state/indexer/sink/psql/psql.go`
- `./state/indexer/sink/psql/psql_test.go`

## Changes
- Updated `toolchain go1.24.4` to `toolchain go1.24.6` in `go.mod`

This is a minimal, surgical change that resolves the security
vulnerability while maintaining full backward compatibility. All tests
pass and the build system works correctly with the updated toolchain.

Fixes #2310.

> [!WARNING]
>
> <details>
> <summary>Firewall rules blocked me from connecting to one or more
addresses</summary>
>
> #### I tried to connect to the following addresses, but was blocked by
firewall rules:
>
> - `vuln.go.dev`
> - Triggering command: `/home/REDACTED/go/bin/govulncheck ./...` (dns
block)
>
> If you need me to access, download, or install something from one of
these locations, you can either:
>
> - Configure [Actions setup
steps](https://gh.io/copilot/actions-setup-steps) to set up my
environment, which run before the firewall is enabled
> - Add the appropriate URLs or hosts to the custom allowlist in this
repository's [Copilot coding agent
settings](https://github.com/celestiaorg/celestia-core/settings/copilot/coding_agent)
(admins only)
>
> </details>



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Co-authored-by: copilot-swe-agent[bot] <[email protected]>
Co-authored-by: rach-id <[email protected]>

Author: Copilot

go.mod

@@ -2,7 +2,7 @@ module github.com/cometbft/cometbft
 
 go 1.24.0
 
-toolchain go1.24.4
+toolchain go1.24.6
 
 require (
 	github.com/BurntSushi/toml v1.4.0