Bump composer/composer from 2.8.12 to 2.9.3 (#4301) #957

Job	Run time
packages_split (bc-installer, bc-installer)	10s
packages_split (bc-favorite, bc-favorite)	11s
packages_split (bc-uploader, bc-uploader)	12s
packages_split (bc-search-index, bc-search-index)	11s
packages_split (BcPluginSample, BcPluginSample)	15s
packages_split (bc-theme-config, bc-theme-config)	11s
packages_split (bc-admin-third, bc-admin-third)	10s
packages_split (bc-content-link, bc-content-link)	9s
packages_split (bc-theme-file, bc-theme-file)	11s
packages_split (bc-front, bc-front)	12s
packages_split (BcThemeSample, BcThemeSample)	11s
packages_split (BcColumn, BcColumn)	14s
packages_split (bc-custom-content, bc-custom-content)	10s
packages_split (bc-blog, bc-blog)	11s
packages_split (bc-seo, bc-seo)	11s
packages_split (bc-editor-template, bc-editor-template)	11s
packages_split (bc-mail, bc-mail)	16s
packages_split (baser-core, baser-core)	14s
packages_split (bc-widget-area, bc-widget-area)	12s
	3m 42s

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