build(deps): bump library/golang from 1.25 to 1.26 in /cmd/external-dns (#2065)

Bumps library/golang from 1.25 to 1.26.

---
updated-dependencies:
- dependency-name: library/golang
  dependency-version: '1.26'
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

cmd/external-dns/Dockerfile

@@ -1,5 +1,5 @@
 # Stage 1: Build
-FROM --platform=${BUILDPLATFORM} docker.io/library/golang:1.25 AS builder
+FROM --platform=${BUILDPLATFORM} docker.io/library/golang:1.26 AS builder
 
 ARG GIT_BUILD_HASH
 ARG TARGETARCH