Directory within subproject cannot share name with subprojects dir

[Ericson2314]

Describe the bug

Suppose my subprojects dir is foo

Suppose one of my subprojects has a dir called foo, e.g. I have something like foo/subproject-a/bar/foo

This should be fine, but it isn't because this code

meson/mesonbuild/interpreter/interpreter.py

Lines 3139 to 3140 in 7396839

	if subproject_dir == norm or subproject_dir in norm.parents:
	raise InterpreterException(f'Sandbox violation: Tried to grab {inputtype} {norm.name} from a nested subproject.')

just looks for any directory name in the path matching the subproject dir name

To Reproduce

We were getting this with Nix, but I have not yet minimized it.

Expected behavior

We should not get confused by names, the sandboxing check should allow this.

system parameters

• Is this a cross build or just a plain native build (for the same computer)?
• what operating system (e.g. MacOS Catalina, Windows 10, CentOS 8.0, Ubuntu 18.04, etc.)
• what Python version are you using e.g. 3.8.0
• what meson --version
• what ninja --version if it's a Ninja build