Fix grammar

[gewarren]

Fast follow to #10803.

[dotnet-policy-service]

Tagging subscribers to this area: @dotnet/area-system-security, @vcsjones

[learn-build-service-prod]

Learn Build status updates of commit ee986fd:

✅ Validation status: passed

File	Status	Preview URL	Details
xml/System.Security.Cryptography.X509Certificates/X509CertificateLoader.xml	✅Succeeded	View

For more details, please refer to the build report.

For any questions, please:

• Try searching the learn.microsoft.com contributor guides
• Post your question in the Learn support channel

[learn-build-service-prod]

Learn Build status updates of commit 95bb533:

✅ Validation status: passed

File	Status	Preview URL	Details
xml/System.Security.Cryptography.X509Certificates/X509CertificateLoader.xml	✅Succeeded	View

For more details, please refer to the build report.

For any questions, please:

• Try searching the learn.microsoft.com contributor guides
• Post your question in the Learn support channel

[learn-build-service-prod]

Learn Build status updates of commit 9b13fd4:

✅ Validation status: passed

File	Status	Preview URL	Details
xml/System.Security.Cryptography.X509Certificates/X509CertificateLoader.xml	✅Succeeded	View

For more details, please refer to the build report.

For any questions, please:

• Try searching the learn.microsoft.com contributor guides
• Post your question in the Learn support channel