Use path separator for git path in transport resources (elastic#133228)

When looking up files from main in transport resources, the system
dependent path is used. However, the beginning slash also needs to be
system dependent.

Author: rjernst

build-tools-internal/src/integTest/groovy/org/elasticsearch/gradle/internal/transport/TransportVersionValidationFuncTest.groovy

@@ -204,18 +204,18 @@ class TransportVersionValidationFuncTest extends AbstractTransportVersionFuncTes
         unreferencedTransportVersion("initial_10.0.0", "10000000")
         latestTransportVersion("10.0", "initial_10.0.0", "10000000")
         when:
-        def result = gradleRunner(":myserver:validateTransportVersionDefinitions").build()
+        def result = gradleRunner(":myserver:validateTransportVersionResources").build()
         then:
-        result.task(":myserver:validateTransportVersionDefinitions").outcome == TaskOutcome.SUCCESS
+        result.task(":myserver:validateTransportVersionResources").outcome == TaskOutcome.SUCCESS
     }
 
     def "named and unreferenced definitions cannot have the same name"() {
         given:
         unreferencedTransportVersion("existing_92", "10000000")
         when:
-        def result = validateDefinitionsFails()
+        def result = validateResourcesFails()
         then:
-        assertDefinitionsFailure(result, "Transport version definition file " +
+        assertValidateResourcesFailure(result, "Transport version definition file " +
                 "[myserver/src/main/resources/transport/definitions/named/existing_92.csv] " +
                 "has same name as unreferenced definition " +
                 "[myserver/src/main/resources/transport/definitions/unreferenced/existing_92.csv]")
@@ -225,8 +225,8 @@ class TransportVersionValidationFuncTest extends AbstractTransportVersionFuncTes
         given:
         unreferencedTransportVersion("initial_10.0.1", "10000001")
         when:
-        def result = gradleRunner(":myserver:validateTransportVersionDefinitions").build()
+        def result = gradleRunner(":myserver:validateTransportVersionResources").build()
         then:
-        result.task(":myserver:validateTransportVersionDefinitions").outcome == TaskOutcome.SUCCESS
+        result.task(":myserver:validateTransportVersionResources").outcome == TaskOutcome.SUCCESS
     }
 }

build-tools-internal/src/main/java/org/elasticsearch/gradle/internal/transport/TransportVersionResourcesService.java

@@ -16,6 +16,7 @@
 import org.gradle.process.ExecResult;
 
 import java.io.ByteArrayOutputStream;
+import java.io.File;
 import java.io.IOException;
 import java.nio.charset.StandardCharsets;
 import java.nio.file.Files;
@@ -199,7 +200,8 @@ private <T> T getMainFile(String resourcePath, BiFunction<String, String, T> par
         if (getMainResources().contains(resourcePath) == false) {
             return null;
         }
-        String content = gitCommand("show", "main:./" + resourcePath).strip();
+
+        String content = gitCommand("show", "main:." + File.separator + resourcePath).strip();
         return parser.apply(resourcePath, content);
     }