Downgrade minio to 7.0.26

minio 7.0.27 requires node < 16.8, breaking compatibility with the
latest LTS version.

We downgrade minio until a fixed version is available.

https://github.com/minio/minio-js/issues/1017
Signed-off-by: David Mehren <git@herrmehren.de>

package.json

@@ -65,7 +65,7 @@
     "meta-marked": "git+https://github.com/hedgedoc/meta-marked",
     "method-override": "^3.0.0",
     "minimist": "^1.2.0",
-    "minio": "^7.0.19",
+    "minio": "7.0.26",
     "moment": "^2.17.1",
     "morgan": "^1.7.0",
     "mysql2": "^2.0.0",