Add upstream testing of the main branch of all supported data backends

[scottyhq]

Is your feature request related to a problem? Please describe.

Adding tests against dependency libraries like xarray and pandas can preemptively catch issues like #563 (which came about due to the latest release of xarray).

Describe the solution you'd like

could modify the current github action (https://github.com/holoviz/hvplot/blob/master/.github/workflows/test.yaml) to use a few different python environment files

For example:
https://github.com/intake/intake-stac/blob/main/.github/workflows/main.yaml

With an 'upstream' environment.yml that installs the main branch of dependency libraries like xarray and pandas. For example:
https://github.com/intake/intake-stac/blob/main/ci/environment-upstream.yml