mkosi: bump fedora from 42 to 43

It seems
- the address sanitizer on fedora 42 reports false-positive, or
- probing partitions in libblkid 2.40.4 has a bug.

Not sure which causes the issue, but anyway the address sanitizer
kills udev-worker when sym_blkid_partition_get_name() is called
in udev-builtin-blkid.c.
```
systemd-udevd[488]: ==488==ERROR: AddressSanitizer: stack-buffer-underflow on address 0x7ffdd716e020 at pc 0x563e3ca66fcb bp 0x7ffdd716d970 sp 0x7ffdd716d968
systemd-udevd[488]: READ of size 8 at 0x7ffdd716e020 thread T0 ((udev-worker))
(snip)
systemd-udevd[488]: HINT: this may be a false positive if your program uses some custom stack unwind mechanism, swapcontext or vfork
systemd-udevd[488]:       (longjmp and C++ exceptions *are* supported)
systemd-udevd[488]: SUMMARY: AddressSanitizer: stack-buffer-underflow (/usr/bin/udevadm+0x187fca) (BuildId: 1fb56dbdf0447aba1185d6e34560b782b76098be)
(snip)
systemd-udevd[488]: Command: (udev-worker)
systemd-udevd[488]: ==488==ABORTING
```

Let's bump fedora from 42 to 43.

Fixes mkosi fedora 42 job failures after c349edfe49.

.github/workflows/mkosi.yml

@@ -110,7 +110,7 @@ jobs:
             no_kvm: 0
             shim: 0
           - distro: fedora
-            release: "42"
+            release: "43"
             runner: ubuntu-24.04
             sanitizers: address,undefined
             llvm: 1