app-misc/ca-certificates: ignore UnicodeEncodeError when opening file

Now that we started encoding strings to unicode by default,
we should also take care of corner cases, where LC_CYPTE is set to a
different value from the systemd default value in `/etc/locale.gen`.

For example, under a build environment with `LC_CTYPE=C`, when the UTF-8
file name is `AC_Ra�z_Certic�mara_S.A..pem`,
build fails like that.

```
Traceback (most recent call last):
  File "/var/tmp/portage/app-misc/ca-certificates-3.27.1-r2/files/certdata2pem.py",
line 127, in <module>
    f = open(fname, 'w')
UnicodeEncodeError: 'ascii' codec can't encode character '\xed' in position 5: ordinal not in range(128)
 * ERROR: app-misc/ca-certificates-3.27.1-r2::coreos failed (compile phase):
```

To fix that, encode filename with system encoding when opening the file.

sdk_container/src/third_party/coreos-overlay/app-misc/ca-certificates/files/certdata2pem.py

@@ -124,7 +124,8 @@ for obj in objects:
             fname = fname.encode('latin1').decode('unicode_escape').encode('latin1').decode('utf8')
         except (UnicodeEncodeError, UnicodeDecodeError):
             pass
-        f = open(fname, 'w')
+
+        f = open(fname.encode(encoding=sys.getfilesystemencoding(), errors="ignore"), 'w')
         f.write("-----BEGIN CERTIFICATE-----\n")
         # obj['CKA_VALUE'] is a string of octals like '\060\311…',
         # with a number not greater than octal 377 (which is 255,