CLDR-18356 exporter:(deps): Bump express from 4.19.2 to 4.21.2 in /tools/st-prom-exporter (#4450)

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]