gdbm: 1.14.1 -> 1.15 (#42263)

Semi-automatic update generated by https://github.com/ryantm/nixpkgs-update tools.

This update was made based on information from https://repology.org/metapackage/gdbm/versions.

These checks were done:

- built on NixOS
- /nix/store/gs61jjz7j3gii2zqm8f65qxpy4k9mybq-gdbm-1.15/bin/gdbmtool passed the binary check.
- /nix/store/gs61jjz7j3gii2zqm8f65qxpy4k9mybq-gdbm-1.15/bin/gdbm_load passed the binary check.
- /nix/store/gs61jjz7j3gii2zqm8f65qxpy4k9mybq-gdbm-1.15/bin/gdbm_dump passed the binary check.
- 3 of 3 passed binary check by having a zero exit code.
- 0 of 3 passed binary check by having the new version present in output.
- found 1.15 with grep in /nix/store/gs61jjz7j3gii2zqm8f65qxpy4k9mybq-gdbm-1.15
- directory tree listing: https://gist.github.com/6bd11a4334992f4b8f19331113c0daa3
- du listing: https://gist.github.com/14f6008edc7f1045329c1205500d1a1a