do not ignore incorrect localCheckoutDir

[jtnord]

Jenkins and plugins versions report

if the local checkout directory is provided but does not exist no error is raised

In reviewing #484 I was alerted to the fact that the pct considers the local checkout directory to not be provided if it does not exist.

This violates the principle of least surprise - it the option is provided yet the path does not exist the pct should return with an error rather than continuing on to test something that may not be what was intended.

What Operating System are you using (both controller, and any agents involved in the problem)?

windows - but this is cross platform.

Reproduction steps

run the pct with the localCheckout option set to a non existant directory

e.g.
java -Xmx1g -jar target\plugins-compat-tester-cli.jar -workDirectory c:\workarea\source\github\cloudbees\unified-release\output-caffeine-api\work -reportFile c:\workarea\source\github\cloudbees\unified-release\output-caffeine-api\out\report.xml -war c:\workarea\source\github\cloudbees\unified-release\products\core-cm\target\core-cm.war -storeAll -fallbackGitHubOrganization jenkinsci-cert -hookPrefixes com.cloudbees.hooks -externalHooksJars c:\workarea\source\github\cloudbees\unified-release\tests\cb-pct-hooks\target\cb-pct-hooks.jar -includePlugins caffeine-api -mavenPropertiesFile c:\workarea\source\github\cloudbees\unified-release\output-caffeine-api\work\maven.properties -mavenProperties jenkins.version=2.375.3-cb-1 -localCheckoutDir c:\workarea\does-not-exist

note that c:\workarea\does-not-exist does not exist :)

Expected Results

pct fails

Actual Results

pct runs and passes

Anything else?

No response