don't clone deprecated blockly levels

[tim-dot-org]

Deprecated blockly levels cause problems when cloned, and should be skipped (here, we return the old blockly level)
Specifically, they cause a validation failure on uniqueness of the level_num field:

code-dot-org/dashboard/app/models/levels/level.rb

Lines 48 to 54 in 5aad68f

	# Together, these validations prevent collisions between level keys, including
	# level keys which differ only by case, between all 3 categories of levels:
	# custom levels, DSLDefined levels, and deprecated blockly levels. For more
	# context on these categories and level keys, see:
	# https://docs.google.com/document/d/1rS1ekCEVU1Q49ckh2S9lfq0tQo-m-G5KJLiEalAzPts/edit
	validates_uniqueness_of :name, case_sensitive: false, conditions: -> {where(level_num: ['custom', nil])}
	validates_uniqueness_of :level_num, scope: :game, conditions: -> {where.not(level_num: ['custom', nil])}

See: https://docs.google.com/document/d/1rS1ekCEVU1Q49ckh2S9lfq0tQo-m-G5KJLiEalAzPts/edit#heading=h.2buyj1ahym0m

Testing story

Couldn't repro locally, but tested with these changes in levelbuilder for pre-express and looks good!

[davidsbailey]

nit: it would be slightly safer to put this before we check for new_name... in the extremely unlikely chance that we end up with a level named blockly_2022 😛 but also in the murkier case which has come up on levelbuilder where some of the blockly levels do actually have names other than "blockly".

the fix looks right to me. it would be nice to still find a way to verify it, but if that proves difficult then a speculative fix could also be ok. in that case it could be enough to convince yourself that you haven't made anything worse locally, even if it doesn't prove things will be fixed on levelbuilder.

[bethanyaconnor]

Looks good to me after addressing Dave's comment. Thanks for working through this!

[tim-dot-org]

tested using these changes on levelbuilder with pre-express and looks good!