ci: ensure macos selected the correct python installed by pyenv

.gitlab-ci.yml

@@ -202,6 +202,10 @@ before_script:
 
 .before_script_macos:
   before_script:
+    # macos is running shell executor, which means it would use
+    # the system installed /usr/local/bin/python3 by default.
+    # Ensure pyenv and PYENV_VERSION installed
+    - eval "$(pyenv init -)"
     - *common-before_scripts
     # On macOS, these tools need to be installed
     - export IDF_TOOLS_PATH="${HOME}/.espressif_runner_${CI_RUNNER_ID}_${CI_CONCURRENT_ID}"

.gitlab/ci/build.yml

@@ -684,6 +684,7 @@ test_build_system_cmake_macos:
     - macos_shell
   variables:
     SHELL_TEST_SCRIPT: test_build_system_cmake.sh
+    PYENV_VERSION: "3.7"
   script:
     - ${IDF_PATH}/tools/ci/test_configure_ci_environment.sh
     - rm -rf test_build_system