test: visual test support compare with a remote branch

[Ovilia]

Brief Information

This pull request is in the type of:

• bug fixing
• new feature
• others

What does this PR do?

Supports using a remote branch on GitHub in visual tests.

Fixed issues

Details

Before: What was the problem?

We can use only a released version or nightly build to do visual tests.

After: How does it behave after the fixing?

We can choose a remote branch on GitHub to do the visual test. This is helpful because I want to compare the changes of a v6 feature and want to compare with v6 branch.

Document Info

One of the following should be checked.

• This PR doesn't relate to document changes
• The document should be updated later
• The document changes have been made in apache/echarts-doc#xxx

Misc

ZRender Changes

• This PR depends on ZRender changes (ecomfe/zrender#xxx).

Related test cases or examples to use the new APIs

N.A.

Others

Merging options

• Please squash the commits into a single one when merging.

Other information

[echarts-bot]

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[github-actions]

The changes brought by this PR can be previewed at: https://echarts.apache.org/examples/editor?version=PR-20676@f0f55f4