build(deps): bump third_party/cctz from `1f2268a` to `306fd9b`

Bumps [third_party/cctz](https://github.com/google/cctz) from `1f2268a` to `306fd9b`.
- [Release notes](https://github.com/google/cctz/releases)
- [Commits](https://github.com/google/cctz/compare/1f2268a1b66f413095a4f3dfc2ff87cbe425fbf4...306fd9b37247a72145ca3f39e59203fb7dfcc890)

---
updated-dependencies:
- dependency-name: third_party/cctz
  dependency-version: 306fd9b37247a72145ca3f39e59203fb7dfcc890
  dependency-type: direct:production
...

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

third_party/cctz

diff --git a/third_party/cctz b/third_party/cctz
index 1f2268a..306fd9b 160000
--- a/third_party/cctz
+++ b/third_party/cctz
@@ -1 +1 @@
-Subproject commit 1f2268a1b66f413095a4f3dfc2ff87cbe425fbf4
+Subproject commit 306fd9b37247a72145ca3f39e59203fb7dfcc890