ci: github: Update for deprecation of add-path

Github has deprecated add-path, so update the workflows that use it to
the new method of setting the PATH.

Signed-off-by: Kumar Gala <kumar.gala@linaro.org>
diff --git a/.github/workflows/doc-build.yml b/.github/workflows/doc-build.yml
index 141442e..ab0c2b9 100644
--- a/.github/workflows/doc-build.yml
+++ b/.github/workflows/doc-build.yml
@@ -12,7 +12,7 @@
     steps:
     - name: Update PATH for west
       run: |
-        echo "::add-path::$HOME/.local/bin"
+        echo "$HOME/.local/bin" >> $GITHUB_PATH
 
     - name: checkout
       uses: actions/checkout@v2
diff --git a/.github/workflows/doc-publish.yml b/.github/workflows/doc-publish.yml
index c83ee00..a31789c 100644
--- a/.github/workflows/doc-publish.yml
+++ b/.github/workflows/doc-publish.yml
@@ -18,7 +18,7 @@
     steps:
     - name: Update PATH for west
       run: |
-        echo "::add-path::$HOME/.local/bin"
+        echo "$HOME/.local/bin" >> $GITHUB_PATH
 
     - name: Determine tag
       id: tag