Bump golang from 1.17.5 to 1.17.6 in /docker

Bumps golang from 1.17.5 to 1.17.6.

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

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

docker/shfmt.dockerfile

@@ -1,4 +1,4 @@
-FROM golang:1.17.5 AS gobuilder
+FROM golang:1.17.6 AS gobuilder
 
 ENV USER=formatter
 ENV UID=10001