.Net: Fix PlannerInstrumentation log message typo (#4904)

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There are two typos in the `PlannerInstrumentation` log message
templates, which causes confusion.

### Description

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These notes will help understanding how your code works. Thanks! -->
Fix the typos.

### Contribution Checklist

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- [ ] The code builds clean without any errors or warnings
- [ ] The PR follows the [SK Contribution
Guidelines](https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md)
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raises no violations
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Co-authored-by: Chris <[email protected]>
Co-authored-by: Gil LaHaye <[email protected]>

Author: 3 people

dotnet/src/InternalUtilities/planning/PlannerInstrumentation.cs

@@ -204,13 +204,13 @@ private static void LogPlanResult(this ILogger logger, object planResult)
     [LoggerMessage(
         EventId = 0,
         Level = LogLevel.Error,
-        Message = "Plan creation failed. Error: {Message}")]
+        Message = "Plan execution failed. Error: {Message}")]
     static partial void LogInvokePlanError(this ILogger logger, Exception exception, string message);
 
     [LoggerMessage(
         EventId = 0,
         Level = LogLevel.Information,
-        Message = "Plan creation duration: {Duration}s.")]
+        Message = "Plan execution duration: {Duration}s.")]
     static partial void LogInvokePlanDuration(this ILogger logger, double duration);
 
 #pragma warning restore SYSLIB1006 // Multiple logging methods cannot use the same event id within a class