CI: Migrate to checkout@v3

Actions runner warns about v2 deprecation

.github/workflows/macos_build.yml

@@ -17,7 +17,7 @@ jobs:
           - "3.11"
     runs-on: macos-11
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
       # Normally, we would use the superbly maintained...
       # - uses: actions/setup-python@v2
       #   with:

.github/workflows/modified_scripts_build.yml

@@ -6,7 +6,7 @@ jobs:
     outputs:
       versions: ${{steps.modified-versions.outputs.versions}}
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
       - run: git fetch origin "$GITHUB_BASE_REF"
       - shell: bash
         run: >
@@ -30,7 +30,7 @@ jobs:
         os: ["macos-11", "macos-12"]
     runs-on: ${{ matrix.os }}
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
       - run: |
           #envvars
           export PYENV_ROOT="$GITHUB_WORKSPACE"
@@ -90,7 +90,7 @@ jobs:
         os: ["ubuntu-20.04", "ubuntu-22.04"]
     runs-on: ${{ matrix.os }}
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
       - run: |
           #envvars
           export PYENV_ROOT="$GITHUB_WORKSPACE"

.github/workflows/pyenv_tests.yml

@@ -16,7 +16,7 @@ jobs:
           - macos-11
     runs-on: ${{ matrix.os }}
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
       # Normally, we would use the superbly maintained...
       # - uses: actions/setup-python@v2
       #   with:

.github/workflows/ubuntu_build.yml

@@ -17,7 +17,7 @@ jobs:
           - "3.11"
     runs-on: ubuntu-22.04
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
       # Normally, we would use the superbly maintained...
       # - uses: actions/setup-python@v2
       #   with: