Fix typos in FromKeyedServicesAttribute.Key documentation remarks

[Copilot]

Fixes two minor typos in the XML documentation remarks for the FromKeyedServicesAttribute.Key property:

• Fixed "value with indicates" → "value indicates"
• Fixed "explict" → "explicit"

The documentation already correctly reflects the breaking change where FromKeyedServicesAttribute.Key became nullable (object?) in .NET 8, including comprehensive remarks explaining when and why the Key can be null for unkeyed services and key inheritance scenarios.

Addresses issue #37143e44 regarding the breaking change documentation for FromKeyedServicesAttribute.Key nullability.

Original prompt

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This section details on the original issue you should resolve

<issue_title>[Breaking change]: FromKeyedServicesAttribute.Key may be null</issue_title>
<issue_description>### Description

FromServiceKeyAttribute has been extended to support null (for unkeyed) and inheritance.

Version

.NET 8

Previous behavior

FromServiceKeyAttribute.Key was a non-nullable object object.

New behavior

FromServiceKeyAttribute.Key is a nullable object object?.

Type of breaking change

• Binary incompatible: Existing binaries might encounter a breaking change in behavior, such as failure to load or execute, and if so, require recompilation.
• Source incompatible: When recompiled using the new SDK or component or to target the new runtime, existing source code might require source changes to compile successfully.
• Behavioral change: Existing binaries might behave differently at run time.

Reason for change

See dotnet/runtime#113585. Support was added for keyed services to annotate parameters as unkeyed.

Recommended action

Adjust any caller that is using FromServiceKeyAttribute to accept a null value for Key.

Feature area

Extensions

Affected APIs

Microsoft.Extensions.DependencyInjection.FromServiceKeyAttribute.Key

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Associated WorkItem - 486863</issue_description>

<agent_instructions>Don't create a breaking change article for this repo. Just update the property's remarks as needed.</agent_instructions>

Comments on the Issue (you are @copilot in this section)

Fixes dotnet/docs#46269

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[BillWagner]

This LGTM. Lets