Changes

feat(tiflow): download exact version content in hotfix branch (#3380)

Over time, the release branch will be continuously updated, and for the
hotfix branch (from the tag), using non-fixed artifacts in integration
testing may lead to test failures due to incompatible changes in
dependency components(tidb & tikv & pd & tiflash). Therefore, we handle
hotfixes separately in the pipeline; when a hotfix branch is detected,
we download and test the dependencies for that tag version.

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Signed-off-by: purelind <purelind@gmail.com>
 (commit: 5aa7227)