Incorrect statement in BigInteger.Pow(BigInteger, Int32) remarks

### Type of issue

Other (describe below)

### Description

The remarks section contains the sentence "If value is negative, the method returns a negative result.". This is incorrect, both with regard to the current implementation and, of course, mathematically.

A correct wording could be "If value is negative _and exponent is odd_, the method returns a negative result.".

### Page URL

https://learn.microsoft.com/en-us/dotnet/api/system.numerics.biginteger.pow?view=net-9.0

### Content source URL

https://github.com/dotnet/dotnet-api-docs/blob/main/xml/System.Numerics/BigInteger.xml

### Document Version Independent Id

69b00605-bab6-902d-ae62-d9175af86096

### Platform Id

d6e01932-bb71-1d15-496c-a3be487079f2

### Article author

@dotnet-bot