chore: bump simplepie/simplepie from 1.5.6 to 1.5.7 in /legacy (#1458)

Bumps [simplepie/simplepie](https://github.com/simplepie/simplepie) from 1.5.6 to 1.5.7.
- [Release notes](https://github.com/simplepie/simplepie/releases)
- [Changelog](https://github.com/simplepie/simplepie/blob/master/CHANGELOG.md)
- [Commits](https://github.com/simplepie/simplepie/compare/1.5.6...1.5.7)

---
updated-dependencies:
- dependency-name: simplepie/simplepie
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

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

legacy/composer.lock

@@ -703,16 +703,16 @@
         },
         {
             "name": "simplepie/simplepie",
-            "version": "1.5.6",
+            "version": "1.5.7",
             "source": {
                 "type": "git",
                 "url": "https://github.com/simplepie/simplepie.git",
-                "reference": "1c68e14ca3ac84346b6e6fe3c5eedf725d0f92c6"
+                "reference": "76be63e72ea6867d9982bf9bd97ba706b196d602"
             },
             "dist": {
                 "type": "zip",
-                "url": "https://api.github.com/repos/simplepie/simplepie/zipball/1c68e14ca3ac84346b6e6fe3c5eedf725d0f92c6",
-                "reference": "1c68e14ca3ac84346b6e6fe3c5eedf725d0f92c6",
+                "url": "https://api.github.com/repos/simplepie/simplepie/zipball/76be63e72ea6867d9982bf9bd97ba706b196d602",
+                "reference": "76be63e72ea6867d9982bf9bd97ba706b196d602",
                 "shasum": ""
             },
             "require": {
@@ -722,7 +722,7 @@
                 "php": ">=5.6.0"
             },
             "require-dev": {
-                "phpunit/phpunit": "~5.4.3 || ~6.5"
+                "yoast/phpunit-polyfills": "^1.0.1"
             },
             "suggest": {
                 "ext-curl": "",
@@ -768,9 +768,9 @@
             ],
             "support": {
                 "issues": "https://github.com/simplepie/simplepie/issues",
-                "source": "https://github.com/simplepie/simplepie/tree/1.5.6"
+                "source": "https://github.com/simplepie/simplepie/tree/1.5.7"
             },
-            "time": "2020-10-14T07:17:22+00:00"
+            "time": "2021-12-19T07:39:23+00:00"
         },
         {
             "name": "zf1s/zend-acl",