fix access_id_CA for trustid-x3-root.signing_policy

Discovered in testing by Diego Davila:
https://opensciencegrid.atlassian.net/browse/SOFTWARE-4436

Apparently i was thrown off by the fact that the other signing
policies in the letsencrypt-certificates repo all had access_id_CA's
that started with /C=US

But it looks like the DST Root CA X3 page only has the /O and /CN parts:
https://ssl-tools.net/subjects/6ff4684d4312d24862819cc02b3d472c1d8a2fa6

trustid-x3-root.signing_policy

@@ -1,3 +1,3 @@
-access_id_CA   X509    '/C=US/O=Digital Signature Trust Co./CN=DST Root CA X3'
+access_id_CA   X509    '/O=Digital Signature Trust Co./CN=DST Root CA X3'
 pos_rights     globus  CA:sign
 cond_subjects  globus  '"/C=US/O=Let\'s Encrypt/CN=Let\'s Encrypt Authority X3" "/C=US/O=Let\'s Encrypt/CN=Let\'s Encrypt Authority X4" "/C=US/O=Let\'s Encrypt/CN=R3" "/C=US/O=Let\'s Encrypt/CN=R4"'