Suppress credscan on test files (#9860)

* Suppress credscan warnings in test files.
* Updates paths in cred suppressions

Author: ryuyu

CredScanSuppressions.json

@@ -0,0 +1,17 @@
+{
+    "tool": "Credential Scanner",
+    "suppressions": [
+        {
+            "file": "tests/NuGetGallery.Facts/Infrastructure/Authentication/ApiKeyV4Facts.cs",
+            "_justification": "Test file containing fake credentials"
+        },
+        {
+            "file": "tests/NuGetGallery.Facts/Infrastructure/Authentication/V3HasherTests.cs",
+            "_justification": "Test file containing fake credentials"
+        },
+        {
+            "file": "tests/NuGetGallery.Facts/Framework/Fakes.cs",
+            "_justification": "Test file containing fake credentials"
+        }
+    ]
+}