[api-ref] Fix HTTP method on the manage API
Should be a POST and not a GET
@@ -409,7 +409,7 @@ Response example
Manage share (since API v2.7)
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-.. rest_method:: GET /v2/{project_id}/shares/manage
+.. rest_method:: POST /v2/{project_id}/shares/manage
.. versionadded:: 2.7
