Bump urllib3 from 1.26.15 to 1.26.18

Bumps [urllib3](https://github.com/urllib3/urllib3) from 1.26.15 to 1.26.18.
- [Release notes](https://github.com/urllib3/urllib3/releases)
- [Changelog](https://github.com/urllib3/urllib3/blob/main/CHANGES.rst)
- [Commits](urllib3/urllib3@1.26.15...1.26.18)

---
updated-dependencies:
- dependency-name: urllib3
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>

requirements.txt

@@ -13,7 +13,7 @@ stix2==3.0.1
 stix2-validator==3.1.3
 toml==0.10.2
 towncrier==22.12.0
-urllib3==1.26.15
+urllib3==1.26.18
 webassets==2.0
 
 # dev dependencies