Fix warning message since m2w64-toolchain is no longer installable

For more context, see the discussion in: https://github.com/conda-forge/pytensor-suite-feedstock/pull/133#issuecomment-2673831166

Fix warning message since m2w64-toolchain is no longer installable
f37380f5 · Ben Mares · Ricardo Vieira · e7dec4d9 · f37380f5
--- a/pytensor/configdefaults.py
+++ b/pytensor/configdefaults.py
@@ -331,7 +331,7 @@ def add_compile_configvars():
                rc = 1
            if rc != 0:
                _logger.warning(
-                    "g++ not available, if using conda: `conda install m2w64-toolchain`"
+                    "g++ not available, if using conda: `conda install gxx`"
                )
    if rc != 0: