Default compat entry for post 1.0 packages should still be `=`

[KristofferC]

Reading this in the README:

This action will modify the compat to:

[compat]
julia = "1.6"
Foo = "~1.2.3"
Bar = "=0.1.2"

This will fail to verify what you want ("When used as part of a testing workflow, this can check that your compat lower bounds are correct."). You might require a bugfix in Foo 1.2.4 (so the Foo = "1.2.3" entry is incorrect) but this would not be discovered in testing using this change to the Project file.