fix: Ensure COMMON_TASK_VALIDATIONS_EXCLUDES_REGEXP works for shfmt

The COMMON_TASK_VALIDATIONS_EXCLUDES_REGEXP values in projects expect to filter the output of 'find', which generally will start with a ./ in the way we use it in this project.  For example, Instrumentor uses "^\.(/get|/metrics-catalog|/test/lib/shunit2)".  But shfmt does *not* have the ./ prefix, so those sorts of expressions will fail to match and exclude necessary files.  Because this variable is also still used to filter the output of find in other tasks (e.g. tflint) we can't change the expectations of what it will be filtering.

Therefore, this:
1. Inserts the leading ./ on each line from shfmt --find ., so as to maintain the API.
2. Fixes the first filter to not exclude anything starting with ., which is now a problem

shellcheck.yml

@@ -4,7 +4,8 @@ shellcheck:
   image: registry.gitlab.com/gitlab-com/gl-infra/common-ci-tasks-images/shellcheck:${GL_ASDF_SHELLCHECK_VERSION}
   script:
     - shfmt --find . |
-      grep -vE "(^|/)(node_modules/|\.)" |
+      xargs -I {} echo "./{}" |
+      grep -vE "(^|/)(node_modules/)" |
       grep -vE "${COMMON_TASK_VALIDATIONS_EXCLUDES_REGEXP:-__ignored__}" |
       xargs shellcheck $SHELLCHECK_ARGS
   after_script: |

shfmt.yml

@@ -7,7 +7,8 @@ shfmt:
   script:
     # Find all *.sh files, and any executable script files
     - shfmt --find . |
-      grep -vE "(^|/)(node_modules/|\.)" |
+      xargs -I {} echo "./{}" |
+      grep -vE "(^|/)(node_modules/)" |
       grep -vE "${COMMON_TASK_VALIDATIONS_EXCLUDES_REGEXP:-__ignored__}" |
       xargs shfmt -w -l -s  -i 2 -d
   after_script: |