Fix regex in build_gdk_image script

What does this MR do and why?

Fix regex in build_gdk_image script

Test

It is easy to test this change locally:

Old regex

set -e

CI_MERGE_REQUEST_TARGET_BRANCH_NAME='17-4-stable-ee'
STABLE_BRANCH_PATTERN="^[\d-]+-stable-ee$"

if [[ $CI_MERGE_REQUEST_TARGET_BRANCH_NAME =~ $STABLE_BRANCH_PATTERN ]]; then
  echo "match"
fi

# Does not return anything
# bash w-dat-test-locally/test-regex.sh

New regex

set -e

CI_MERGE_REQUEST_TARGET_BRANCH_NAME='17-4-stable-ee'
STABLE_BRANCH_PATTERN="^[0-9-]+-stable-ee$"

if [[ $CI_MERGE_REQUEST_TARGET_BRANCH_NAME =~ $STABLE_BRANCH_PATTERN ]]; then
  echo "match"
fi

# bash w-dat-test-locally/test-regex.sh
match

References

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• gitlab-com/gl-infra/delivery#20782 (closed)

MR acceptance checklist

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