Resolve warning re use of `kwargs.data`

[dmbates]

In Julia v1.8.0-rc4 creating a DictTable produces a warning of the form

┌ Warning: use values(kwargs) and keys(kwargs) instead of kwargs.data and kwargs.itr
│   caller = #DictTable#117 at DictTable.jl:31 [inlined]
└ @ Core ~/.julia/packages/TypedTables/zfbS2/src/DictTable.jl:31

[codecov[bot]]

Codecov Report

Merging #96 (5e98c60) into main (a7ca98c) will not change coverage. The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main      #96   +/-   ##
=======================================
  Coverage   69.63%   69.63%           
=======================================
  Files           7        7           
  Lines         909      909           
=======================================
  Hits          633      633           
  Misses        276      276           

Impacted Files	Coverage Δ
src/DictTable.jl	57.78% <100.00%> (ø)

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[dmbates]

I noticed in the testing output that similar changes should be made in lines 27 and 28 of src/FlexTable.jl but I'm not sure if I can add those changes to this PR.

[stuartthomas25]

There is a similar error in FlexTable.jl