fix: EXPOSED-412 Remove all the usage of isOldMySql function in tests

[obabichevjb]

The main purpose of this PR is to remove usage of isOldMySql() function, because now there are different enum constants for different MySql versions in TestDB.

Some other changes:

• the tests excluded for MySql V8 were rechecked and fixed if it's possible.
• usages of TestDB.MARIADB were replaced with TestDB.ALL_MARIADB to find failed tests faster if we add different versions for MariaDB
• TestDB.ALL* constants are Sets now. Idea always suggests to convert Lists with these constants into Sets, so it should make Idea complain less.

[joc-a]

Suggestion: It's minor, but how about we rename the bit for MySQL 5 in build.gradle.kts like this?

testDb("mysql5") {                           
    port = 3001                             
    dialects("MYSQL_V5")                    
    dependencies {                          
        dependency(rootProject.libs.mysql51)
    }                                       
}

[bog-walk]

Thanks for cleaning all this up. Please see small comments.