root: Patch range restriction and gcc lower bound (spack#48449)

* root: Restrict patch range

* root: Set minimum gcc version for cxxstd=20

* root: fix gcc range when cxxstd 20

Co-authored-by: Paul Gessinger <hello@paulgessinger.com>

---------

Co-authored-by: Wouter Deconinck <wdconinc@gmail.com>

var/spack/repos/builtin/packages/root/package.py

@@ -142,7 +142,7 @@ class Root(CMakePackage):
     patch(
         "https://github.com/root-project/root/commit/2f00d6df258906c1f6fe848135a88b836db3077f.patch?full_index=1",
         sha256="8da36032082e65ae246c03558a4c3fd67b157d1d0c6d20adac9de263279d1db6",
-        when="@6.28:6.28.12",
+        when="@6.28.6:6.28.12",
     )
     patch(
         "https://github.com/root-project/root/commit/14838b35600b08278e69bc3d8d8669773bc11399.patch?full_index=1",
@@ -452,6 +452,8 @@ class Root(CMakePackage):
         "cxxstd=20", when="@:6.28.02", msg="C++20 support requires root version at least 6.28.04"
     )
 
+    conflicts("%gcc@:10", when="cxxstd=20")
+
     # See https://github.com/root-project/root/issues/11128
     conflicts("%clang@16:", when="@:6.26.07", msg="clang 16+ support was added in root 6.26.08")