ensure correct order of DOM insertions with neighbouring keyed each blocks

[Rich-Harris]

fixes #1306

[codecov-io]

Codecov Report

Merging #1309 into master will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master    #1309   +/-   ##
=======================================
  Coverage   91.51%   91.51%           
=======================================
  Files         124      124           
  Lines        4417     4417           
  Branches     1390     1390           
=======================================
  Hits         4042     4042           
  Misses        154      154           
  Partials      221      221

Impacted Files	Coverage Δ
src/generators/nodes/EachBlock.ts	97.63% <100%> (ø)	⬆️

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