[Release-only] Update runtime doc code links to point to 0.6 (#10023)

https://pytorch.org/executorch/0.6/using-executorch-runtime-integration.html
https://pytorch.org/executorch/0.6/using-executorch-cpp.html

Author: lucylq

docs/source/using-executorch-cpp.md

@@ -64,7 +64,7 @@ The `executor_runner` target is built by default when building with CMake. It ca
 ./cmake-out/executor_runner --model_path path/to/model.pte
 ```
 
-The runner source code can be found in the ExecuTorch repo under [examples/portable/executor_runner.cpp](https://github.com/pytorch/executorch/blob/main/examples/portable/executor_runner/executor_runner.cpp). Some backends, such as CoreML, have dedicated runners to showcase backend and platform-specific functionality. See [examples/apple/coreml](https://github.com/pytorch/executorch/tree/main/examples/apple/coreml) and the [examples](https://github.com/pytorch/executorch/tree/main/examples) directory for more information.
+The runner source code can be found in the ExecuTorch repo under [examples/portable/executor_runner.cpp](https://github.com/pytorch/executorch/blob/release/0.6/examples/portable/executor_runner/executor_runner.cpp). Some backends, such as CoreML, have dedicated runners to showcase backend and platform-specific functionality. See [examples/apple/coreml](https://github.com/pytorch/executorch/tree/release/0.6/examples/apple/coreml) and the [examples](https://github.com/pytorch/executorch/tree/release/0.6/examples) directory for more information.
 
 ## Next Steps
 

docs/source/using-executorch-runtime-integration.md

@@ -27,7 +27,7 @@ For non-POSIX-compliant systems, a minimal no-op PAL implementation is provided.
 Overriding the default PAL implementation is commonly done to route logs to a user-specified destination or to provide PAL functionality on embedded systems. To override one or more PAL methods, take the following steps:
 
 - Include
-  [`executorch/runtime/platform/platform.h`](https://github.com/pytorch/executorch/blob/main/runtime/platform/platform.h)
+  [`executorch/runtime/platform/platform.h`](https://github.com/pytorch/executorch/blob/release/0.6/runtime/platform/platform.h)
   in one of your application's `.c` or `.cpp` files.
 - Define an implementation of one or more of the `et_pal_*()` functions.
 
@@ -36,7 +36,7 @@ definition can override them at link time. To ensure that your definitions take
 precedence, you may need to ensure that the strong definitions precede the weak
 definitions in the link order.
 
-See [runtime/platform/platform.h](https://github.com/pytorch/executorch/blob/main/runtime/platform/platform.h) for the PAL function signatures and [runtime/platform/default/posix.cpp](https://github.com/pytorch/executorch/blob/main/runtime/platform/default/posix.cpp) for the reference POSIX implementation.
+See [runtime/platform/platform.h](https://github.com/pytorch/executorch/blob/release/0.6/runtime/platform/platform.h) for the PAL function signatures and [runtime/platform/default/posix.cpp](https://github.com/pytorch/executorch/blob/release/0.6/runtime/platform/default/posix.cpp) for the reference POSIX implementation.
 
 ## Kernel Libraries