Bump golang in /.github/dockerfile-for-dependabot

Bumps golang from 1.18.2-alpine to 1.18.3-alpine.

---
updated-dependencies:
- dependency-name: golang
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>

.github/dockerfile-for-dependabot/Dockerfile

@@ -1,2 +1,2 @@
 # Used for dependabot to detect new golang versions
-FROM golang:1.18.2-alpine
+FROM golang:1.18.3-alpine