Enable two additional hooks from default pre-commit-hooks

Enabled 'check-case-conflict' because of our mixed Linux and macOS development.
Although APFS supports case-sensitive containers, it is not the default as far
as I am aware. Linux filesystems are typically case-sensitive however.

With the merge of https://github.com/cisagov/development-guide/pull/42 we now
have a TOML file in a repository, so it does not hurt to add this hook in case
more are added in the future.

.pre-commit-config.yaml

@@ -7,9 +7,11 @@ repos:
   - repo: https://github.com/pre-commit/pre-commit-hooks
     rev: v3.2.0
     hooks:
+      - id: check-case-conflict
       - id: check-executables-have-shebangs
       - id: check-json
       - id: check-merge-conflict
+      - id: check-toml
       - id: check-xml
       - id: debug-statements
       - id: detect-aws-credentials