Avoid filename conflicts on case-insensitive filesystems

Fixes https://bugs.archlinux.org/task/66812

Testing:

1. pip install --user . installs ~/.local/bin/{namcap,parsepkgbuild}
2. https://aur.archlinux.org/packages/namcap-git (with patches for this branch) installs /usr/bin/{namcap,parsepkgbuild}

As a side note, here is the PKGBUILD patch for namcap-git I used for testing:

diff --git a/PKGBUILD b/PKGBUILD
index 3ac84c4..b6a15c4 100644
--- a/PKGBUILD
+++ b/PKGBUILD
@@ -17,7 +17,7 @@ makedepends=('git' 'python-setuptools')
 checkdepends=('systemd')
 provides=("${pkgname%-git}")
 conflicts=("${pkgname%-git}")
-source=("$pkgname::git+$url.git")
+source=("$pkgname::git+https://gitlab.archlinux.org/yan12125/namcap.git#branch=fix-filename-case-conflicts")
 sha256sums=('SKIP')
 
 pkgver() {
@@ -36,7 +36,7 @@ check() {
   cd $pkgname
 
   env PARSE_PKGBUILD_PATH="$srcdir/${pkgname}" \
-      PATH="$srcdir/${pkgname}:$PATH" \
+      PATH="$srcdir/${pkgname}/bin:$PATH" \
       python setup.py test
 }