Fix missing dash in --ignore-exit-code flag (#45812)

Author: flibustier7seas

docs/core/testing/microsoft-testing-platform-intro.md

@@ -251,7 +251,7 @@ The list below described only the platform options. To see the specific options
 
   Prints out a description of how to use the command.
 
-- **`-ignore-exit-code`**
+- **`--ignore-exit-code`**
 
   Allows some non-zero exit codes to be ignored, and instead returned as `0`. For more information, see [Ignore specific exit codes](./microsoft-testing-platform-exit-codes.md#ignore-specific-exit-codes).