Minor fix in dynamic template validation

[javanna]

As part of #66156 the validation of dynamic templates has been adapted to support runtime fields. As part of that change, a break was forgotten, which causes needless additional validation rounds after a template has been already successfully validated against one of the field types.

[elasticmachine]

Pinging @elastic/es-search (Team:Search)

[javanna]

I am fixing this same issue for 7.x as part of #66156 , the backport of the PR that introduced the problem, which does cause problems in 7.x due to deprecation warnings.

[romseygeek]

LGTM, although trying to understand that outer loop is giving me a headache. Given that a DynamicTemplate can only have one fieldtype, maybe we should rework this in a followup so that templates themselves are responsible for validation?

[javanna]

@romseygeek I am not sure there is a way around that loop. When a template is not mapped against a specific type (because match_mapping_type is * or not specified), we try to validate it against all possible dynamic field types, and if at least one does not throw error, we accept the template, although it may actually cause problems at index time depending on the field it gets applied to in practice.

[javanna]

run elasticsearch-ci/eql-correctness