Bump dnslib from 0.9.25 to 0.9.26 in /tools

Bumps [dnslib](https://github.com/paulc/dnslib) from 0.9.25 to 0.9.26.
- [Release notes](https://github.com/paulc/dnslib/releases)
- [Commits](paulc/dnslib@0.9.25...0.9.26)

---
updated-dependencies:
- dependency-name: dnslib
  dependency-version: 0.9.26
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

tools/serve/requirements_dns.txt

@@ -1 +1 @@
-dnslib==0.9.25
+dnslib==0.9.26