ci: move checkers build to Fedora:38 (#12738)

We need to ignore some "unreachable code" warnings in ShellCheck because
the functions are called after being exported.

Author: coryan

ci/cloudbuild/builds/check-api.sh

@@ -1,4 +1,5 @@
 #!/bin/bash
+# shellcheck disable=SC2317
 #
 # Copyright 2021 Google LLC
 #

ci/cloudbuild/builds/publish-docs.sh

@@ -1,4 +1,5 @@
 #!/bin/bash
+# shellcheck disable=SC2317
 #
 # Copyright 2021 Google LLC
 #

ci/cloudbuild/dockerfiles/checkers.Dockerfile

@@ -17,7 +17,7 @@
 # than to the extent that certain distros offer certain versions of software
 # that the build needs. It's fine to add more deps that are needed by the
 # `checkers.sh` build.
-FROM fedora:37
+FROM fedora:38
 ARG NCPU=4
 ARG ARCH=amd64