release 2.6.4 candidate 2

[andreasabel]

Commits:

• Change version 2.6.4 to 2.6.3.20230924 (2.6.4 RC2)
• Agda.cabal: change -Werror to -Wwarn
• Release-2.6.4: remove test-suite

Candidate at: https://hackage.haskell.org/package/Agda-2.6.3.20230914/candidate

Changes over release candidate 1

Regressions reported for RC1

• #6758: Agda still blocks on instantiated meta
• #6759: Agda 2.6.4 RC1 fails to terminate type checking

Fixes in new features of Agda 2.6.4

• #6757: Incorrect InteractionMetaBoundaries warning
• #6802: Incorrect warning for module inside an opaque block
• #6805: Types of opaque definitions can be inferred
• #6807: Caching is broken in the presence of opaque

Further fixes

• #6269: Documentation is missing for --keep-covering-clauses and --lossy-unification
• #6750: Order of deserialization depends on build of Agda (version of hashable)
• #6786: Missing "when checking parameters of module M" in error message
• #6787: Refine doesn't find proof of refl=refl without K
• #6794: Safe Agda accepts {-# TERMINATING #-} pragma in interleaved mutual block
• #6795: Missing warning about discarded {-# TERMINATING #-} pragma in where block inside interleaved mutual block
• #6823: Suboptimal error location for missing definition before mutual block