What's the issue you encountered?

Dev warning - Legacy Tags detected. Please migrate your 'forge' namespace tags to the 'c' namespace! See net.neoforged.neoforge.common.Tags.java for all tags.
NOTE: Many tags have been moved around or renamed. Some new ones were added so please review the new tags.
And make sure you follow tag conventions for new tags! The convention is c with nouns generally being plural and adjectives being singular.
You can disable this message in NeoForge's common config by setting logLegacyTagWarnings to "SILENCED" or see individual tags with "DEV_VERBOSE".

Legacy tags:
TagKey[minecraft:worldgen/biome / forge:is_magical] -> TagKey[minecraft:worldgen/biome / c:is_magical]
TagKey[minecraft:worldgen/biome / forge:is_lush] -> TagKey[minecraft:worldgen/biome / c:is_lush]
TagKey[minecraft:worldgen/biome / forge:is_sparse/overworld] -> TagKey[minecraft:worldgen/biome / c:is_sparse_vegetation/overworld]
TagKey[minecraft:worldgen/biome / forge:is_mushroom] -> TagKey[minecraft:worldgen/biome / c:is_mushroom]
TagKey[minecraft:worldgen/biome / forge:is_cold/end] -> TagKey[minecraft:worldgen/biome / c:is_cold/end]
TagKey[minecraft:worldgen/biome / forge:is_coniferous] -> TagKey[minecraft:worldgen/biome / c:is_tree/coniferous]
TagKey[minecraft:worldgen/biome / forge:is_plateau] -> TagKey[minecraft:worldgen/biome / c:is_plateau]
TagKey[minecraft:worldgen/biome / forge:is_dry/nether] -> TagKey[minecraft:worldgen/biome / c:is_dry/nether]
TagKey[minecraft:worldgen/biome / forge:is_dry/overworld] -> TagKey[minecraft:worldgen/biome / c:is_dry/overworld]
TagKey[minecraft:worldgen/biome / forge:is_spooky] -> TagKey[minecraft:worldgen/biome / c:is_spooky]
TagKey[minecraft:worldgen/biome / forge:is_mountain] -> TagKey[minecraft:worldgen/biome / c:is_mountain]
TagKey[minecraft:worldgen/biome / forge:is_dry/end] -> TagKey[minecraft:worldgen/biome / c:is_dry/end]
TagKey[minecraft:worldgen/biome / forge:is_rare] -> TagKey[minecraft:worldgen/biome / c:is_rare]
TagKey[minecraft:worldgen/biome / forge:is_cold/overworld] -> TagKey[minecraft:worldgen/biome / c:is_cold/overworld]
TagKey[minecraft:worldgen/biome / forge:is_sandy] -> TagKey[minecraft:worldgen/biome / c:is_sandy]
TagKey[minecraft:worldgen/biome / forge:is_cave] -> TagKey[minecraft:worldgen/biome / c:is_cave]
TagKey[minecraft:worldgen/biome / forge:is_desert] -> TagKey[minecraft:worldgen/biome / c:is_desert]
TagKey[minecraft:worldgen/biome / forge:is_plains] -> TagKey[minecraft:worldgen/biome / c:is_plains]
TagKey[minecraft:worldgen/biome / forge:is_underground] -> TagKey[minecraft:worldgen/biome / c:is_underground]
TagKey[minecraft:worldgen/biome / forge:is_hot/nether] -> TagKey[minecraft:worldgen/biome / c:is_hot/nether]
TagKey[minecraft:worldgen/biome / forge:is_wet/overworld] -> TagKey[minecraft:worldgen/biome / c:is_wet/overworld]
TagKey[minecraft:worldgen/biome / forge:is_wasteland] -> TagKey[minecraft:worldgen/biome / c:is_wasteland]
TagKey[minecraft:worldgen/biome / forge:is_swamp] -> TagKey[minecraft:worldgen/biome / c:is_swamp]
TagKey[minecraft:worldgen/biome / forge:is_snowy] -> TagKey[minecraft:worldgen/biome / c:is_snowy]
TagKey[minecraft:worldgen/biome / forge:is_dense/overworld] -> TagKey[minecraft:worldgen/biome / c:is_dense_vegetation/overworld]
TagKey[minecraft:worldgen/biome / forge:is_hot/overworld] -> TagKey[minecraft:worldgen/biome / c:is_hot/overworld]
TagKey[minecraft:item / forge:sandstone] -> TagKey[minecraft:item / c:sandstone/blocks]
TagKey[minecraft:item / forge:music_discs] -> See similar c tags in NeoForge's Tags class
TagKey[minecraft:item / forge:fence_gates/wooden] -> TagKey[minecraft:item / c:fence_gates/wooden]
TagKey[minecraft:item / forge:mushrooms] -> TagKey[minecraft:item / c:mushrooms]
TagKey[minecraft:item / forge:sand] -> TagKey[minecraft:item / c:sands]
TagKey[minecraft:item / forge:fences/wooden] -> TagKey[minecraft:item / c:fences/wooden]
TagKey[minecraft:block / forge:fences/wooden] -> TagKey[minecraft:block / c:fences/wooden]
TagKey[minecraft:block / forge:sand] -> TagKey[minecraft:block / c:sands]
TagKey[minecraft:block / forge:dirt] -> See similar c tags in NeoForge's Tags class
TagKey[minecraft:block / forge:sandstone] -> TagKey[minecraft:block / c:sandstone/blocks]
TagKey[minecraft:block / forge:fence_gates/wooden] -> TagKey[minecraft:block / c:fence_gates/wooden]

How can the issue be reproduced?

(no action needed. above is printed in log)

Logs

No response

Mod Version

21.0.0.7

Additional information

No response