Revert "Pin Prettier plug-in version in GitHub action (#351)"
Revert "Pin Prettier plug-in version in GitHub action (#351)"

This reverts commit c44313b54f18fd2adc0442f158b4d822df4c3293.

[prettier/plugin-xml](https://github.com/prettier/plugin-xml) restored support for the `xmlSelfClosingSpace` option with https://github.com/prettier/plugin-xml/pull/300 for [v1.1.0](https://github.com/prettier/plugin-xml/blob/main/CHANGELOG.md#110---2021-09-26), which allows formatting checks to complete successfully.

This commit unpins the plug-in version now that the regression in https://github.com/prettier/plugin-xml/issues/11 is resolved, so the latest version of the plug-in can once again be used.

Signed-off-by: Roger Sheen <a61a1add71dadc74037ae5e44ee30713db9a7451@infotexture.net>

dita-ot/docs