Update mysql

Changes:

- https://github.com/docker-library/mysql/commit/3607c86: Update to 5.6.49-1debian9
- https://github.com/docker-library/mysql/commit/01a4869: Update to 8.0.21-1debian10
- https://github.com/docker-library/mysql/commit/a6b87c5: Update to 5.7.31-1debian10

library/mysql

@@ -4,14 +4,14 @@ Maintainers: Tianon Gravi <[email protected]> (@tianon),
              Joseph Ferguson <[email protected]> (@yosifkit)
 GitRepo: https://github.com/docker-library/mysql.git
 
-Tags: 8.0.20, 8.0, 8, latest
-GitCommit: bc6e37a2bed792b1c4fc6ab1ec3ce316e6a5f061
+Tags: 8.0.21, 8.0, 8, latest
+GitCommit: 01a48696e18aa6372cc47c57e9217af0b35b93bf
 Directory: 8.0
 
-Tags: 5.7.30, 5.7, 5
-GitCommit: bc6e37a2bed792b1c4fc6ab1ec3ce316e6a5f061
+Tags: 5.7.31, 5.7, 5
+GitCommit: a6b87c55ecdf9426d42ff7814be7e9b1fc33b292
 Directory: 5.7
 
-Tags: 5.6.48, 5.6
-GitCommit: bc6e37a2bed792b1c4fc6ab1ec3ce316e6a5f061
+Tags: 5.6.49, 5.6
+GitCommit: 3607c86e534658529a638e7616bfc1e02528e667
 Directory: 5.6