Fix referencing another schema file relative to CWD

After the switch to github.com/santhosh-tekuri/jsonschema/v6 we noticed that one of our charts was failing with the following error:

> Error: values don't meet the specifications of the schema(s) in the following chart(s):
> my-chart:
> failing loading "file://./schema/library.json": open /schema/library.json: no such file or directory

Checking against helm v3.18.4 (the last version of helm to use the old jsonschema module) everything worked as expected.

From what I can tell, the newly adopted jsonschema module automatically prefixes "file://" onto the schema path, and any references within the main values.schema.json

This commit, as best as I can test, puts back the behaviour found in v3.18.4 where executing a helm subcommand that validates against a values.schema.json file it follows references to additional schema files.

Signed-off-by: Ben Lavery-Griffiths <ben@lavery-griffiths.com>

pkg/chart/common/util/jsonschema.go

@@ -131,12 +131,12 @@ func ValidateAgainstSingleSchema(values common.Values, schemaJSON []byte) (reter
 
 	compiler := jsonschema.NewCompiler()
 	compiler.UseLoader(loader)
-	err = compiler.AddResource("file:///values.schema.json", schema)
+	err = compiler.AddResource("./values.schema.json", schema)
 	if err != nil {
 		return err
 	}
 
-	validator, err := compiler.Compile("file:///values.schema.json")
+	validator, err := compiler.Compile("./values.schema.json")
 	if err != nil {
 		return err
 	}
@@ -165,7 +165,7 @@ func (e JSONSchemaValidationError) Error() string {
 
 	// This string prefixes all of our error details. Further up the stack of helm error message
 	// building more detail is provided to users. This is removed.
-	errStr = strings.TrimPrefix(errStr, "jsonschema validation failed with 'file:///values.schema.json#'\n")
+	errStr = strings.TrimPrefix(errStr, "jsonschema validation failed with './values.schema.json#'\n")
 
 	// The extra new line is needed for when there are sub-charts.
 	return errStr + "\n"