[biocswirl][fix] Fix github actions matrix formatting

[lisancao]

[biocswirl][fix] Fix github actions matrix formatting

We are getting syntax errors from our actions workflow file, resulting in failures in our workflow runs (https://github.com/biocswirl-dev-team/automated_testing/actions). This is expected as the workflow was written pretty ad-hoc, but we do need to get this working. Goal is to at least get a successful check.

Tasks

• Use github actions YAML linter or manually debug .github/workflows/mergecheck.yml

Resources

https://github.com/cschleiden/actions-linter
https://github.com/s-u/pkg-check-test
https://github.com/r-lib/actions

Tag can be

biocswirl(related to course material)
biocterm (interface changes)
dev      (developers only)
file     (changes to file and folder structuring) 
rpkg     (r package/usethis and CRAN documentation changes)
feat     (new feature)
fix      (bug fix)
refactor (refactoring code)
style    (formatting, missing semi colons, etc; no code change)
doc      (changes to documentation)
test     (adding or refactoring tests; no production code change)
version  (version bump/new release; no production code change)
dbg      (Changes in debugging code/frameworks; no production code change)
license  (Edits regarding licensing; no production code change)
hack     (Temporary fix to make things move forward; please avoid it)
WIP      (Work In Progress; for intermediate commits to keep patches reasonably sized)