You have to do the Ability Check.
The rule in the DMG (page 200) that you quoted has the solution (emphasis mine):
If the spell is on your class’s spell list but of a higher level than you can normally cast, you must make an ability check using your spellcasting ability to determine whether you cast it successfully. The DC equals 10 + spell’s level. On a failed check, the spell disappears from the scroll with no other effect.
Take a look at the rules for multiclassing in PHB (page 164) too (emphasis mine):
If you have more than one spellcasting class, this table might give you spell slots of a level that is higher than the spells you know or can prepare. You can use those slots, but only to cast your Lower-level spells.
Here, since you have two different spell lists (which may overlap, in this case):
- Druid’s list, you known and can prepare spells up to 5th level
- Cleric’s list, you known and can prepare spells up to 1st level
Since you total level is 10 (or 11$^1$), you have 5th spell slots available, but you can cast only 1st level spells from the cleric’s list. If you try to cast a Cleric spell of level greater than 1 from a scroll, then the enlighten part of the rule for casting from a scroll applies: the spell is in your class list, but it has an higher level than the one you can normally cast as a cleric, not as a character of level 10 (or 11).
$^1$ Depending on your Druid level when you decided to multiclass.