Remove platform requirement

This requirement might exist to prevent contributors from committing
something incompatible with the lowest supported version of PHP to the
lock file, thus breaking the "locked" jobs.

Author: greg0ire

.github/workflows/continuous-integration.yml

@@ -92,6 +92,10 @@ jobs:
           echo "COMPOSER_ROOT_VERSION=${{ inputs.composer-root-version }}" >> $GITHUB_ENV
         if: "${{ inputs.composer-root-version }}"
 
+      - name: "Remove platform requirement"
+        run: "composer config --unset platform"
+        if: "${{ matrix.dependencies == 'highest' }}"
+
       - name: "Install dependencies with Composer"
         uses: "ramsey/composer-install@v2"
         with: