ci: Add `checkov` to `.tool-versions`.

This is to prevent Renovate from updating mise while its registry is still broken.

.gitlab-ci-asdf-versions.yml

 # DO NOT MANUALLY EDIT; Run ./scripts/update-asdf-version-variables.sh to update this
 variables:
+    GL_ASDF_CHECKOV_VERSION: 3.2.358
     GL_ASDF_PRE_COMMIT_VERSION: 4.1.0
     GL_ASDF_SHELLCHECK_VERSION: 0.10.0
     GL_ASDF_SHFMT_VERSION: 3.10.0

.gitlab-ci-default-asdf-versions.yml

 # DO NOT MANUALLY EDIT; Run ./scripts/update-asdf-version-variables.sh to update this
 variables:
+    GL_COMMON_CI_TASKS_DEFAULT_ASDF_CHECKOV_VERSION: 3.2.358
     GL_COMMON_CI_TASKS_DEFAULT_ASDF_PRE_COMMIT_VERSION: 4.1.0
     GL_COMMON_CI_TASKS_DEFAULT_ASDF_SHELLCHECK_VERSION: 0.10.0
     GL_COMMON_CI_TASKS_DEFAULT_ASDF_SHFMT_VERSION: 3.10.0

.tool-versions

 # For first-time installation, you'll need to install all plugins:
 # Use the script: ./scripts/install-asdf-plugins.sh
 # NOTE: please add new plugins to ./scripts/install-asdf-plugins.sh when adding items here
+checkov 3.2.358
 pre-commit 4.1.0 # datasource=github-releases depName=pre-commit/pre-commit
 python system
 shellcheck 0.10.0 # datasource=github-releases depName=koalaman/shellcheck