draco: make 'ghc-filesystem' a build dependency

[nilason]

Description

Make dracos dependency ghc-filesystem a build dependency.

Closes: https://trac.macports.org/ticket/69738

Type(s)

• bugfix
• enhancement
• security fix

Tested on

macOS x.y
Xcode x.y / Command Line Tools x.y.z

Verification

Have you

• followed our Commit Message Guidelines?
• squashed and minimized your commits?
• checked that there aren't other open pull requests for the same change?
• referenced existing tickets on Trac with full URL in commit message?
• checked your Portfile with port lint --nitpick?
• tried existing tests with sudo port test?
• tried a full install with sudo port -vst install?
• tested basic functionality of all binary files?
• checked that the Portfile's most important variants haven't been broken?

[reneeotten]

You're removing a library dependency and should thus increase the "revision"

[nilason]

You're removing a library dependency and should thus increase the "revision"

According to MacPorts Guide, that usually shouldn't be needed when

changing a dependency's type, e.g. from depends_lib to depends_build

which is the case here.