Sync mpdf in composer.lock (#3091)

Composer was complaining locally.

composer.lock

@@ -4,7 +4,7 @@
         "Read more about it at https://getcomposer.org/doc/01-basic-usage.md#installing-dependencies",
         "This file is @generated automatically"
     ],
-    "content-hash": "61d142fc39389fd47139c4dc6f572d6b",
+    "content-hash": "60da78cdd66329fbd4e0d50324363072",
     "packages": [
         {
             "name": "ezyang/htmlpurifier",
@@ -1390,16 +1390,16 @@
         },
         {
             "name": "mpdf/mpdf",
-            "version": "v8.1.1",
+            "version": "v8.1.2",
             "source": {
                 "type": "git",
                 "url": "https://github.com/mpdf/mpdf.git",
-                "reference": "e511e89a66bdb066e3fbf352f00f4734d5064cbf"
+                "reference": "a8a22f4874157e490d41b486053a20bec42e182c"
             },
             "dist": {
                 "type": "zip",
-                "url": "https://api.github.com/repos/mpdf/mpdf/zipball/e511e89a66bdb066e3fbf352f00f4734d5064cbf",
-                "reference": "e511e89a66bdb066e3fbf352f00f4734d5064cbf",
+                "url": "https://api.github.com/repos/mpdf/mpdf/zipball/a8a22f4874157e490d41b486053a20bec42e182c",
+                "reference": "a8a22f4874157e490d41b486053a20bec42e182c",
                 "shasum": ""
             },
             "require": {
@@ -1463,7 +1463,7 @@
                     "type": "custom"
                 }
             ],
-            "time": "2022-04-18T11:50:28+00:00"
+            "time": "2022-08-15T08:15:09+00:00"
         },
         {
             "name": "myclabs/deep-copy",
@@ -5274,5 +5274,5 @@
         "ext-zlib": "*"
     },
     "platform-dev": [],
-    "plugin-api-version": "2.3.0"
+    "plugin-api-version": "2.2.0"
 }