Fix isinstance check and broadened tests to include more Python versions

[cwognum]

Changelogs

• Fixes error with graphium-train finetuning #439 by changing an isinstance check that uses Python syntax that was not supported before Python 3.10.
• Expanded the tests to also run on Python 3.8 and 3.9, so that we catch issues like these fast and early next time.

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Checklist:

• Was this PR discussed in an issue? It is recommended to first discuss a new feature into a GitHub issue before opening a PR.
• Add tests to cover the fixed bug(s) or the new introduced feature(s) (if appropriate).
• Update the API documentation is a new function is added, or an existing one is deleted.
• Write concise and explanatory changelogs above.
• If possible, assign one of the following labels to the PR: feature, fix or test (or ask a maintainer to do it for you).

[codecov]

Codecov Report

Merging #442 (7a6a722) into main (4adaaf7) will decrease coverage by 0.04%.
The diff coverage is 66.66%.

@@            Coverage Diff             @@
##             main     #442      +/-   ##
==========================================
- Coverage   65.56%   65.52%   -0.04%     
==========================================
  Files          90       90              
  Lines        8226     8218       -8     
==========================================
- Hits         5393     5385       -8     
  Misses       2833     2833              

Flag	Coverage Δ
unittests	65.52% <66.66%> (-0.04%)	⬇️

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Components	Coverage Δ
ipu	49.14% <ø> (ø)