Fix GH-11054: Reset OpenSSL errors when using a PEM public key

The error happens when the PEM contains a public key, as it will be
first tried to be parsed as a certificate. The parsing

Fix GH-11054: Reset OpenSSL errors when using a PEM public key

The error happens when the PEM contains a public key, as it will be
first tried to be parsed as a certificate. The parsing as a certificate
fails, which then leads to a corresponding error tracked by PHP with
the next call to php_openssl_store_errors().

This change introduces an error marking to be able to reset the stored
errors to the state before trying the certificate.

Closes GH-11055

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