Apply latest env variables in github host runner to fix CI (#1334)

Currently we are using `ANDROID_HOME` and `ANDROID_NDK_LATEST_HOME`.
All variables should follow definitions in https://github.com/actions/virtual-environments/blob/main/images/linux/Ubuntu2004-Readme.md#environment-variables-3

doc/build_wamr.md

@@ -527,13 +527,13 @@ able to generate a shared library support Android platform.
 - look for a command named *sdkmanager* and download below components. version numbers might need to check and pick others
    - "build-tools;29.0.3"
    - "cmake;3.10.2.4988404"
-   - "ndk;21.0.6113669"
+   - "ndk;latest"
    - "patcher;v4"
    - "platform-tools"
    - "platforms;android-29"
 - add bin/ of the downloaded cmake to $PATH
-- export ANDROID_SDK_HOME=/the/path/of/downloaded/sdk/
-- export ANDROID_NDK_HOME=/the/path/of/downloaded/sdk/ndk/
+- export ANDROID_HOME=/the/path/of/downloaded/sdk/
+- export ANDROID_NDK_LATEST_HOME=/the/path/of/downloaded/sdk/ndk/2x.xxx/
 - ready to go
 
 Use such commands, you are able to compile with default configurations. Any compiling requirement should be satisfied by modifying product-mini/platforms/android/CMakeList.txt. For example, chaning ${WAMR_BUILD_TARGET} in CMakeList could get different libraries support different ABIs.

product-mini/platforms/android/CMakeLists.txt

@@ -6,9 +6,11 @@ cmake_minimum_required (VERSION 3.4.1)
 set (CMAKE_VERBOSE_MAKEFILE on)
 set (CMAKE_BUILD_TYPE       Release)
 
-set (CMAKE_TOOLCHAIN_FILE "$ENV{ANDROID_NDK_HOME}/build/cmake/android.toolchain.cmake")
-set (ANDROID_NDK $ENV{ANDROID_NDK_HOME})
-set (ANDROID_SDK $ENV{ANDROID_SDK_HOME})
+# https://github.com/actions/virtual-environments/blob/main/images/linux/Ubuntu2004-Readme.md#environment-variables-3
+set (CMAKE_TOOLCHAIN_FILE "$ENV{ANDROID_NDK_LATEST_HOME}/build/cmake/android.toolchain.cmake")
+set (ANDROID_SDK $ENV{ANDROID_HOME})
+set (ANDROID_NDK $ENV{ANDROID_NDK_LATEST_HOME})
+
 set (ANDROID_ABI "x86")
 set (ANDROID_LD lld)
 if (NOT DEFINED ANDROID_PLATFORM)