Fix doxygen action

- Fix checkout error: `fatal: destination path '.' already exists and is not an empty directory.`
- Remove `GITHUB_SHA` in env, because set automatically
  https://help.github.com/en/articles/virtual-environments-for-github-actions#environment-variables
- Change minute from 0 to 20 for test soon

.github/workflows/doxygen.yml

@@ -1,7 +1,7 @@
 name: doxygen
 on:
   schedule:
-    - cron: '0 * * * *'
+    - cron: '20 * * * *'
 
 jobs:
   latest:
@@ -9,62 +9,46 @@ jobs:
     steps:
       - name: Download current index.html
         run: |
-          mkdir -p tmp
-          curl -o tmp/index.html https://rubyci.s3.amazonaws.com/doxygen-latest-html/index.html || touch tmp/index.html
+          curl -o /tmp/index.html https://rubyci.s3.amazonaws.com/doxygen-latest-html/index.html || touch /tmp/index.html
       - name: Install libraries
         run: |
           set -x
-          if grep -q "${GITHUB_SHA}" tmp/index.html; then exit; fi
+          if grep -q "${GITHUB_SHA}" /tmp/index.html; then exit; fi
           sudo sed /etc/apt/sources.list -e "s/^# deb-src/deb-src/g" -i
           sudo apt-get update
           sudo apt-get install ruby2.5 doxygen graphviz
           sudo apt-get build-dep ruby2.5
-        env:
-          GITHUB_SHA: ${{ github.sha }}
 
       # Not using official actions/checkout because it's unstable and sometimes doesn't work for a fork.
       - name: Checkout ruby/ruby
         run: |
-          if grep -q "${GITHUB_SHA}" tmp/index.html; then exit; fi
+          if grep -q "${GITHUB_SHA}" /tmp/index.html; then exit; fi
           git clone --depth=10 https://github.com/ruby/ruby . && git reset --hard "$GITHUB_SHA"
-        env:
-          GITHUB_SHA: ${{ github.sha }}
 
       - name: Fixed world writable dirs
         run: |
-          if grep -q "${GITHUB_SHA}" tmp/index.html; then exit; fi
+          if grep -q "${GITHUB_SHA}" /tmp/index.html; then exit; fi
           chmod go-w $HOME
           sudo chmod -R go-w /usr/share
-        env:
-          GITHUB_SHA: ${{ github.sha }}
       - run: |
-          if grep -q "${GITHUB_SHA}" tmp/index.html; then exit; fi
+          if grep -q "${GITHUB_SHA}" /tmp/index.html; then exit; fi
           autoconf
-        env:
-          GITHUB_SHA: ${{ github.sha }}
       - name: Configure
         run: |
-          if grep -q "${GITHUB_SHA}" tmp/index.html; then exit; fi
+          if grep -q "${GITHUB_SHA}" /tmp/index.html; then exit; fi
           ./configure
-        env:
-          GITHUB_SHA: ${{ github.sha }}
       - name: Generate Doxyfile
         run: |
-          if grep -q "${GITHUB_SHA}" tmp/index.html; then exit; fi
+          if grep -q "${GITHUB_SHA}" /tmp/index.html; then exit; fi
           make Doxyfile
-        env:
-          GITHUB_SHA: ${{ github.sha }}
       - name: Run Doxygen
         run: |
-          if grep -q "${GITHUB_SHA}" tmp/index.html; then exit; fi
+          if grep -q "${GITHUB_SHA}" /tmp/index.html; then exit; fi
           doxygen
-        env:
-          GITHUB_SHA: ${{ github.sha }}
       - name: Upload results
         run: |
-          if grep -q "${GITHUB_SHA}" tmp/index.html; then exit; fi
+          if grep -q "${GITHUB_SHA}" /tmp/index.html; then exit; fi
           aws s3 sync doc/capi/html/ s3://rubyci/doxygen-latest-html
         env:
-          GITHUB_SHA: ${{ github.sha }}
           AWS_ACCESS_KEY_ID: ${{ secrets.AWS_ACCESS_KEY_ID }}
           AWS_SECRET_ACCESS_KEY: ${{ secrets.AWS_SECRET_ACCESS_KEY }}