fix(antd/next): fix array string field addition logic

[janryWang]

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What have you changed?

Fixed #2983

[codecov]

Codecov Report

Merging #2998 (e2c67f6) into formily_next (378496b) will not change coverage.
The diff coverage is n/a.

@@              Coverage Diff              @@
##           formily_next    #2998   +/-   ##
=============================================
  Coverage         96.06%   96.06%           
=============================================
  Files               149      149           
  Lines              6488     6488           
  Branches           1750     1750           
=============================================
  Hits               6233     6233           
  Misses              255      255           

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[github-actions]

Size Change: -50 B (0%)

Total Size: 505 kB

Filename	Size	Change
packages/antd/dist/formily.antd.umd.development.js	71.2 kB	-9 B (0%)
packages/antd/dist/formily.antd.umd.production.js	39.8 kB	-2 B (0%)
packages/next/dist/formily.next.umd.development.js	76.1 kB	-34 B (0%)
packages/next/dist/formily.next.umd.production.js	44.2 kB	-5 B (0%)

ℹ️ View Unchanged

Filename	Size
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packages/vue/dist/formily.vue.umd.development.js	16.4 kB
packages/vue/dist/formily.vue.umd.production.js	9.75 kB

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