raise ValueError for unsupported name attribute value tags

[dxbjavid]

Parsing an X.509 name attribute whose value carries an ASN.1 tag outside the recognised string types looked the tag up in the _ASN1_TYPE_TO_ENUM dict without handling a miss, so a crafted certificate, CSR, CRL or OCSP response made accessing subject or issuer raise a bare KeyError rather than the ValueError every other malformed-input path raises. The value itself is already accepted into the catch-all AnyString variant, so only the type lookup was left unguarded. I map the miss to an invalid-value parse error so it surfaces as a ValueError with the usual field location, and add a regression test that mutates a built certificate's commonName tag.