Allocations in LSR1 push!

MRE
```
using LinearOperators
using LinearAlgebra

lsr1_op = LSR1Operator(Float64, 10)
y1 = randn(10)
s1 = randn(10)

println(@allocated push!(lsr1_op, y1, s1))

y2 = randn(10)
s2 = randn(10)

println(@allocated push!(lsr1_op, y2, s2))
```
results in
```
288
720
```