Fix setting commit & vendor variables via make

[rcoup]

087db1d (#4911) bumped the git-lfs Go package version to v3, but the variables being set in the Makefile for GitCommit & Vendor didn't change, which meant setting them had no effect. Fix this by updating the variable paths.

In addition, quote the Vendor variable so it can have spaces in it.

Before (main@ d3716c9):

$ make bin/git-lfs VENDOR=WorldOfGooCorp
...
GOOS= GOARCH= go build -ldflags="-X github.com/git-lfs/git-lfs/config.Vendor=WorldofGooCorp -X github.com/git-lfs/git-lfs/config.GitCommit=d3716c90 -s -w " -gcflags=" " -trimpath -o ./bin/git-lfs ./git-lfs.go
$ bin/git-lfs version
git-lfs/3.2.0 (GitHub; darwin arm64; go 1.19.1)

$ make bin/git-lfs "VENDOR=World of Goo Corporation"
...
GOOS= GOARCH= go build -ldflags="-X github.com/git-lfs/git-lfs/config.Vendor=World of Goo Corporation -X github.com/git-lfs/git-lfs/config.GitCommit=d3716c90 -s -w " -gcflags=" " -trimpath -o ./bin/git-lfs ./git-lfs.go
# command-line-arguments
usage: link [options] main.o
...
make: *** [Makefile:318: bin/git-lfs] Error 2

After:

$ make bin/git-lfs "VENDOR=World of Goo Corporation"
...
GOOS= GOARCH= go build -ldflags="-X 'github.com/git-lfs/git-lfs/v3/config.Vendor=World of Goo Corporation' -X github.com/git-lfs/git-lfs/v3/config.GitCommit=8d300427 -s -w " -gcflags=" " -trimpath -o ./bin/git-lfs ./git-lfs.go
$ bin/git-lfs version
git-lfs/3.2.0 (World of Goo Corporation; darwin arm64; go 1.19.1; git 8d300427)

[bk2204]

This looks good. Thanks for the patch.

[bk2204]

The CI fix is #5142.