fix(test): set MySQL credentials file permissions in combined config tests

The MySQL receiver validates that passfiles have 0600 or 0400 permissions
for security. Git doesn't preserve file permissions beyond the executable
bit, so checked-out files default to 0644 in CI, causing test failures.

Add os.Chmod(0600) calls in TestCombinedV1V2EC2Config and
TestCombinedV1V2EKSConfig before config translation to ensure the
.mysql_credentials testdata file has the required restrictive permissions.

This matches the existing fix in TestDBIMySQLConfigLinux and ensures
tests pass reliably in CI and local development environments.

Author: Klarsen04

translator/tocwconfig/tocwconfig_unix_test.go

@@ -144,13 +144,17 @@ func TestJournaldLogsUnitsAndPriority(t *testing.T) {
 func TestCombinedV1V2EC2Config(t *testing.T) {
 	resetContext(t)
 	context.CurrentContext().SetMode(config.ModeEC2)
+	// Fix MySQL credentials file permissions (required by receiver validation)
+	require.NoError(t, os.Chmod("sampleConfig/opentelemetry/testdata/.mysql_credentials", 0600))
 	checkTranslation(t, "opentelemetry/combined_v1_v2_ec2_config", "linux", nil, "")
 }
 
 func TestCombinedV1V2EKSConfig(t *testing.T) {
 	resetContext(t)
 	context.CurrentContext().SetMode(config.ModeEC2)
 	context.CurrentContext().SetKubernetesMode(config.ModeEKS)
+	// Fix MySQL credentials file permissions (required by receiver validation)
+	require.NoError(t, os.Chmod("sampleConfig/opentelemetry/testdata/.mysql_credentials", 0600))
 
 	// Cannot use checkTranslation here because the container_insights prometheus
 	// receiver references /var/run/secrets/kubernetes.io/serviceaccount/token