Fix two CMake errors

[hageboeck]

• The first error fixed is an unquoted variable that creates an error in the case that the remote repos of roottest are not called origin. It's relatively common to give the remotes useful names, and those users shouldn't be punished with weird errors.
• Re-enable FindGLEW. ROOT claims that the latest version of CMake has an error in FindGLEW. In fact, the error was fixed after cmake 3.25, so we can use system GLEW again starting from 3.26

[github-actions[bot]]

Test Results

    18 files      18 suites   3d 19h 29m 50s ⏱️  2 700 tests  2 698 ✅ 1 💤 1 ❌ 46 147 runs  46 146 ✅ 0 💤 1 ❌

For more details on these failures, see this check.

Results for commit 68b13ab7.

:recycle: This comment has been updated with latest results.

[hageboeck]

I would still think we need to address: https://github.com/root-project/root/pull/16465/files#r1767367204

I think that's done. It now configures with:

  -- 191/247 python tutorials have been activated.
- error: No such remote 'origin'
+ -- Searching for "origin" repo of roottest: error: No such remote 'origin'
  -- Found roottest: /Users/shageboeck/code/root-src/../roottest

What do you think @pcanal ?