Bump actions/setup-python from 2 to 4 (AtsushiSakai#871)

Bumps [actions/setup-python](https://github.com/actions/setup-python) from 2 to 4.
- [Release notes](https://github.com/actions/setup-python/releases)
- [Commits](actions/setup-python@v2...v4)

---
updated-dependencies:
- dependency-name: actions/setup-python
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

.github/workflows/Linux_CI.yml

@@ -21,7 +21,7 @@ jobs:
     - run: git fetch --prune --unshallow
 
     - name: Setup python
-      uses: actions/setup-python@v2
+      uses: actions/setup-python@v4
       with:
         python-version: ${{ matrix.python-version }}
     - name: Install dependencies

.github/workflows/MacOS_CI.yml

@@ -26,7 +26,7 @@ jobs:
         run: brew install bash
 
       - name: Setup python
-        uses: actions/setup-python@v2
+        uses: actions/setup-python@v4
         with:
           python-version: ${{ matrix.python-version }}
 

.github/workflows/Windows_CI.yml

@@ -23,7 +23,7 @@ jobs:
       - run: git fetch --prune --unshallow
 
       - name: Setup python
-        uses: actions/setup-python@v2
+        uses: actions/setup-python@v4
         with:
           python-version: ${{ matrix.python-version }}
 

.github/workflows/gh-pages.yml

@@ -8,7 +8,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
     - name: Setup python
-      uses: actions/setup-python@v3
+      uses: actions/setup-python@v4
     - name: Checkout
       uses: actions/checkout@master
       with: