Update to Go 1.26.3 (#261)

This change bumps the toolchain version and also enables dependabot
updates for e2e tests.

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## Summary by CodeRabbit

* **Chores**
* Updated Go toolchain to a newer version for improved stability and
performance
* Enhanced automated dependency management configuration for development
and testing environments

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.github/dependabot.yaml

@@ -19,3 +19,13 @@ updates:
       k8s:
         patterns:
           - "k8s.io/*"
+  - package-ecosystem: "gomod"
+    directories:
+      - "/test/e2e"
+    schedule:
+      interval: "weekly"
+    open-pull-requests-limit: 15
+    groups:
+      gomod-e2e:
+        patterns:
+          - "*"

go.mod

@@ -2,7 +2,7 @@ module github.com/netbirdio/kubernetes-operator
 
 go 1.26.0
 
-toolchain go1.26.2
+toolchain go1.26.3
 
 require (
 	github.com/fluxcd/pkg/runtime v0.106.0

test/e2e/go.mod

@@ -2,7 +2,7 @@ module github.com/netbirdio/kubernetes-operator/test/e2e
 
 go 1.26.0
 
-toolchain go1.26.2
+toolchain go1.26.3
 
 require (
 	github.com/go-openapi/testify/v2 v2.5.0