fix build warning (#786)

Author: tg123

tests/KubernetesClient.Tests/CertUtilsTests.cs

@@ -30,7 +30,7 @@ public void LoadFromFiles()
 
             // Just validate that this doesn't throw and private key is non-null
             var cert = CertUtils.GeneratePfx(cfg);
-            Assert.NotNull(cert.PrivateKey);
+            Assert.NotNull(cert.GetRSAPrivateKey());
         }
 
         /// <summary>
@@ -45,7 +45,7 @@ public void LoadFromFilesRelativePath()
 
             // Just validate that this doesn't throw and private key is non-null
             var cert = CertUtils.GeneratePfx(cfg);
-            Assert.NotNull(cert.PrivateKey);
+            Assert.NotNull(cert.GetRSAPrivateKey());
         }
 
         /// <summary>
@@ -59,7 +59,7 @@ public void LoadFromInlineData()
 
             // Just validate that this doesn't throw and private key is non-null
             var cert = CertUtils.GeneratePfx(cfg);
-            Assert.NotNull(cert.PrivateKey);
+            Assert.NotNull(cert.GetRSAPrivateKey());
         }
 
         /// <summary>
@@ -74,7 +74,7 @@ public void LoadFromInlineDataRelativePath()
 
             // Just validate that this doesn't throw and private key is non-null
             var cert = CertUtils.GeneratePfx(cfg);
-            Assert.NotNull(cert.PrivateKey);
+            Assert.NotNull(cert.GetRSAPrivateKey());
         }
 
         /// <summary>