Drop PHP 7.4 support for master (26)

Signed-off-by: Côme Chilliet <come.chilliet@nextcloud.com>

composer.json

 		"optimize-autoloader": true,
 		"sort-packages": true,
 		"platform": {
-			"php": "7.4"
+			"php": "8.0"
 		},
 		"allow-plugins": {
 			"bamarni/composer-bin-plugin": true
 		}
 	},
 	"require": {
+		"php": "^8.0",
 		"ext-json": "*",
 		"ext-libxml": "*",
 		"ext-mbstring": "*",

lib/versioncheck.php

  * along with this program. If not, see <http://www.gnu.org/licenses/>.
  *
  */
-// Show warning if a PHP version below 7.4 is used,
-if (PHP_VERSION_ID < 70400) {
+// Show warning if a PHP version below 8.0 is used,
+if (PHP_VERSION_ID < 80000) {
 	http_response_code(500);
-	echo 'This version of Nextcloud requires at least PHP 7.4<br/>';
+	echo 'This version of Nextcloud requires at least PHP 8.0<br/>';
 	echo 'You are currently running ' . PHP_VERSION . '. Please update your PHP version.';
 	exit(1);
 }