Remove test with Guzzle 6 version

Author: Rodion Liuborets

.github/workflows/tests.yaml

@@ -57,34 +57,6 @@ jobs:
 
       - run: composer test
 
-  guzzle:
-    name: Unit Tests With Guzzle 6 (php ${{ matrix.php-version }})
-    runs-on: ubuntu-latest
-    # always run on push events
-    # only run on pull_request_target event when pull request pulls from fork repository
-    if: >
-      github.event_name == 'push' || 
-      github.event_name == 'pull_request_target' && github.event.pull_request.head.repo.full_name != github.repository 
-    strategy:
-      fail-fast: false
-      matrix:
-        php-version: [ 7.4 ]
-
-    steps:
-      - uses: actions/checkout@v2
-
-      - uses: shivammathur/[email protected]
-        with:
-          php-version: ${{ matrix.php-version }}
-
-      - run: composer require guzzlehttp/guzzle "^6.5"
-
-      - run: composer self-update
-
-      - run: composer install --no-interaction --prefer-source --dev
-
-      - run: composer test
-
   protobuf:
     name: Unit Tests With Protobuf C Extension 3.13 (php ${{ matrix.php-version }})
     runs-on: ubuntu-latest