`+(::BlockVector, ::Vector)` promotes axis from `BlockedOneTo` to `BlockedUnitRange`

[lassepe]

As the title says:

using BlockArrays: mortar

julia> a = rand(4)
4-element Vector{Float64}:
 0.8245882057036666
 0.6496327699506389
 0.2058423091408491
 0.22035347885553225

julia> b = mortar([rand(2), rand(2)])
2-blocked 4-element BlockVector{Float64}:
 0.21798163954085292
 0.5995732233841912 
 ───────────────────
 0.7830701187033979 
 0.662908943211767  

julia> a + b
2-blocked 4-element BlockVector{Float64, Vector{Vector{Float64}}, Tuple{BlockedUnitRange{Int64, Vector{Int64}}}}:
 1.0425698452445196
 1.24920599333483  
 ──────────────────
 0.988912427844247 
 0.8832624220672992

The result of a + b should have the same axis type as b. I noticed this because I had a vector c = [b] and couldn't push a + b into c because the types don't match.