SslStreamCertificateContext stops fetching OCSP staples after one request failure

[rzikm]

Related to #89907. The fix (#90200) prevents the invalid OCSP staple from being sent out, but the _pendingDownload field is never cleared which prevents the code from fetching another OCSP staple in the future.

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Issue Details

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Related to #89907. The fix (#90200) prevents the invalid OCSP staple from being sent out, but the _pendingDownload field is never cleared which prevents the code from fetching another OCSP staple in the future.

Author:	rzikm
Assignees:	-
Labels:	area-System.Net.Security, untriaged, needs-area-label
Milestone:	-