Define gen_exclude anchor at first use to resolve warning

This was the warning:

[WARNING] Unexpected key(s) present at root: gen_exclude

Also fix the regex: the old pattern was missing the ^ before the second alternative

Author: rwgk

.pre-commit-config.yaml

@@ -12,8 +12,6 @@ ci:
     skip: [bandit]
     submodules: false
 
-gen_exclude: &gen_exclude '^cuda_bindings/cuda/bindings/.*\.in?$|cuda_bindings/docs/source/module/.*\.rst?$'
-
 # Please update the rev: SHAs below with this command:
 # pre-commit autoupdate --freeze
 repos:
@@ -54,7 +52,7 @@ repos:
     - id: check-yaml
     - id: debug-statements
     - id: end-of-file-fixer
-      exclude: *gen_exclude
+      exclude: &gen_exclude '^(?:cuda_bindings/cuda/bindings/.*\.in?|cuda_bindings/docs/source/module/.*\.rst?)$'
     - id: mixed-line-ending
     - id: requirements-txt-fixer
     - id: trailing-whitespace