chore(deps): update go toolchain directive to v1.26.3 (#318)

| datasource     | package | from   | to     |
| -------------- | ------- | ------ | ------ |
| golang-version | go      | 1.26.2 | 1.26.3 |

Signed-off-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>
Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

go.mod

@@ -2,7 +2,7 @@ module github.com/cloudnative-pg/cnpg-i
 
 go 1.25.0
 
-toolchain go1.26.2
+toolchain go1.26.3
 
 require (
 	google.golang.org/grpc v1.81.0