Bump pylibmc from 1.6.1 to 1.6.3 in /requirements

Bumps [pylibmc](https://github.com/lericson/pylibmc) from 1.6.1 to 1.6.3.
- [Release notes](https://github.com/lericson/pylibmc/releases)
- [Changelog](https://github.com/lericson/pylibmc/blob/master/docs/changelog.rst)
- [Commits](lericson/pylibmc@1.6.1...1.6.3)

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

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

Author: dependabot[bot]

requirements/prod.txt

@@ -1,6 +1,6 @@
 -r common.txt
 django-pylibmc==0.6.1
 django-redis-cache==3.0.1
-pylibmc==1.6.1
+pylibmc==1.6.3
 redis==5.0.7
 sentry-sdk==1.44.1