Knowing next to nothing about Perforce, it appears at least this odd-sounding behavior can be overridden, but whether you have access to do this is another matter as it's probably server-side:
https://stackoverflow.com/questions/48195633/prevent-perforce-from-marking-files-as-read-only
Seems there is also an option to check out a whole project which would I assume then make all files RW (which Godot should have no issue with) and be in line with how your VCS works: "Checkout All in Project to check out the project file and all files in the project" which may be what you need? https://www.perforce.com/manuals/p4vs/Content/P4VS/managing.editing.html
I can't imagine it is a good idea to try and workaround the behavior defined by your VCS. I mean, it's entirely possible if you do not 'checkout' the file that it simply is no longer tracked (I'd have to RTM to confirm), so overriding the RO manually is gonna result in a bad time. Should also clarify this file locking behavior sounds like it would impact far more programs than Godot, so I'd probably confirm with your lecturer first and ask them how it should be done before trying to work around it. If you DID want to try working around it, you could just set up a bash/batch script to alter file permissions before opening Godot, but I seriously wouldn't risk it if it means you could arbitrarily lose work.
Could you alternatively use GIT within Perforce instead (sounds like there is integration with 'Helix4Git' if available)?
Does seem like a crazy design decision. Were I speccing a VCS for soon to be employed students, I would base it on what is almost unequivocally the most popular VCS system used across workplaces to give them the best chance of experiencing what they will likely actually end up using, which also happens to be opensource . . .