Stop relying on actions/checkout

because it randomly fails on authorization like:
https://github.com/ruby/ruby/runs/190887455
Also the backoff seems too short. Maybe we need tool/travis_retry.sh for
this too.

Cloning ruby/ruby does not need authorization. We don't need to use
actions/checkout.

.github/workflows/macos.yml

@@ -21,10 +21,8 @@ jobs:
         run: |
           brew update
           brew install gdbm gmp libffi openssl zlib ccache autoconf automake libtool readline
-      - name: Checkout
-        uses: actions/checkout@master
-        with:
-          fetch-depth: 50
+      - name: Checkout # not using actions/checkout because it's unstable.
+        run: tool/ci_retry.sh git clone --depth=50 https://github.com/ruby/ruby .
       - name: Set ENV
         run: |
           echo '##[set-env name=JOBS]'-j$((1 + $(sysctl -n hw.activecpu)))

.github/workflows/ubuntu.yml

@@ -20,10 +20,8 @@ jobs:
           sudo apt-get update
           sudo apt-get install ruby2.5
           sudo apt-get build-dep ruby2.5
-      - name: Checkout
-        uses: actions/checkout@master
-        with:
-          fetch-depth: 50
+      - name: Checkout # not using actions/checkout because it's unstable.
+        run: tool/ci_retry.sh git clone --depth=50 https://github.com/ruby/ruby .
       - name: Set ENV
         run: |
           export JOBS=-j$((1 + $(nproc --all)))

.travis.yml

@@ -91,10 +91,10 @@ env:
     #     sources:
     #       - ubuntu-toolchain-r-test
     before_install:
-      - tool/travis_retry.sh sudo -E apt-add-repository -y "ppa:ubuntu-toolchain-r/test"
-      - tool/travis_retry.sh bash -c "sudo rm -rf '${TRAVIS_ROOT}/var/lib/apt/lists/'* && sudo apt-get update -yq"
+      - tool/ci_retry.sh sudo -E apt-add-repository -y "ppa:ubuntu-toolchain-r/test"
+      - tool/ci_retry.sh bash -c "sudo rm -rf '${TRAVIS_ROOT}/var/lib/apt/lists/'* && sudo apt-get update -yq"
       - |-
-        tool/travis_retry.sh sudo -E apt-get $travis_apt_get_options install \
+        tool/ci_retry.sh sudo -E apt-get $travis_apt_get_options install \
           gcc-8 \
           libffi-dev \
           libgdbm-dev \
@@ -119,9 +119,9 @@ env:
         config:
           retries: true
     before_install:
-      - tool/travis_retry.sh bash -c "sudo rm -rf '${TRAVIS_ROOT}/var/lib/apt/lists/'* && sudo apt-get update -yq"
+      - tool/ci_retry.sh bash -c "sudo rm -rf '${TRAVIS_ROOT}/var/lib/apt/lists/'* && sudo apt-get update -yq"
       - |-
-        tool/travis_retry.sh sudo -E apt-get $travis_apt_get_options install \
+        tool/ci_retry.sh sudo -E apt-get $travis_apt_get_options install \
           clang-8 \
           llvm-8-tools \
           libffi-dev \
@@ -277,10 +277,10 @@ env:
     #     sources:
     #       - ubuntu-toolchain-r-test
     before_install:
-      - tool/travis_retry.sh sudo -E apt-add-repository -y "ppa:ubuntu-toolchain-r/test"
-      - tool/travis_retry.sh bash -c "sudo rm -rf '${TRAVIS_ROOT}/var/lib/apt/lists/'* && sudo apt-get update -yq"
+      - tool/ci_retry.sh sudo -E apt-add-repository -y "ppa:ubuntu-toolchain-r/test"
+      - tool/ci_retry.sh bash -c "sudo rm -rf '${TRAVIS_ROOT}/var/lib/apt/lists/'* && sudo apt-get update -yq"
       - |-
-        tool/travis_retry.sh sudo -E apt-get $travis_apt_get_options install \
+        tool/ci_retry.sh sudo -E apt-get $travis_apt_get_options install \
           gcc-8-multilib \
           libffi-dev:i386 \
           libffi6:i386 \

tool/ci_retry.sh

@@ -1,6 +1,8 @@
 #!/bin/sh -eu
 # The modified version of `travis_retry` to support custom backoffs, which is used by .travis.yml.
 # https://github.com/travis-ci/travis-build/blob/master/lib/travis/build/bash/travis_retry.bash
+#
+# Now this is also used by .github/workflow/*.yml.
 
 for sleep in 0 ${WAITS:- 1 25 100}; do
   sleep "$sleep"