ci: Update FreeBSD image to 13.2

```
pkg install -y git
Updating FreeBSD repository catalogue...
pkg: http://pkgmir.geo.freebsd.org/FreeBSD:12:amd64/quarterly/meta.txz: Not Found
repository FreeBSD has no meta file, using default settings
pkg: http://pkgmir.geo.freebsd.org/FreeBSD:12:amd64/quarterly/packagesite.pkg: Not Found
pkg: http://pkgmir.geo.freebsd.org/FreeBSD:12:amd64/quarterly/packagesite.txz: Not Found
Unable to update repository FreeBSD
Error updating repositories!
```

Author: taiki-e

.cirrus.yml

@@ -14,7 +14,7 @@ env:
 freebsd_task:
   name: test ($TARGET)
   freebsd_instance:
-    image_family: freebsd-12-4
+    image_family: freebsd-13-2
   matrix:
     - env:
         TARGET: x86_64-unknown-freebsd