Fix parsing error when finding an existing GMT in macos

[ZMAlt]

I found a fault when I set up the environment to debug external calls. See #1723.

Steps:

1. compile GMT using Xcode
2. set $GMT_LIBRARY to /Users/zm/Desktop/git/gmt/xbuild/src/Debug/libgmt.dylib (path of gmtlib compiled using Xcode)
3. set ENV["SYSTEMWIDE_GMT"] = 1 in julia-repl
4. using Pkg; Pkg.build("GMT")

However, the build can't parse the correct path of gdal (mebrew/opt/gdal/lib/libgdal.36.dylib) due to the wrong index. So I remove it in this PR.

julia> Pkg.build("GMT")
    Building GMT → `~/.julia/scratchspaces/44cfe95a-1eb2-52ea-b672-e2afdf69b78f/c584158f845b3ae7ce51df9cd677bc1c5edff29a/build.log`

shell> cat ~/.julia/scratchspaces/44cfe95a-1eb2-52ea-b672-e2afdf69b78f/c584158f845b3ae7ce51df9cd677bc1c5edff29a/build.log
error: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/otool-classic: can't open file: mebrew/opt/gdal/lib/libgdal.36.dylib (No such file or directory)
ProcessFailedException(Base.Process[Process(`otool -L mebrew/opt/gdal/lib/libgdal.36.dylib`, ProcessExited(1)), Process(`grep libproj`, ProcessExited(1))])

No GMT system wide installation found

[joa-quim]

OK, I don't remember anymore why I had that indices and it works for you.

Don't understand why the tests are failing. It looks like from where it was launched it has no access to the SECRET that is used to create the ~./cdsapirc file.