Bump shivammathur/setup-php from 2.7.0 to 2.8.0

Bumps [shivammathur/setup-php](https://github.com/shivammathur/setup-php) from 2.7.0 to 2.8.0.
- [Release notes](https://github.com/shivammathur/setup-php/releases)
- [Commits](shivammathur/setup-php@2.7.0...a67fcb9)

Signed-off-by: dependabot[bot] <support@github.com>

.github/workflows/CI.yml

@@ -22,7 +22,7 @@ jobs:
           auth_header="$(git config --local --get http.https://github.com/.extraheader)"
           git submodule sync
           git -c "http.extraheader=$auth_header" -c protocol.version=2 submodule update --init --force --depth=1
-      - uses: shivammathur/setup-php@2.7.0
+      - uses: shivammathur/setup-php@2.8.0
         with:
           php-version: ${{ matrix.php-versions }}
           extension: mbstring
@@ -43,7 +43,7 @@ jobs:
     name: Code quality
     steps:
       - uses: actions/checkout@v2
-      - uses: shivammathur/setup-php@2.7.0
+      - uses: shivammathur/setup-php@2.8.0
         with:
           php-version: '7.4'
           extension: mbstring