ci: harden repository security analysis (#3186)

Co-authored-by: savasp-agent[bot] <275188714+savasp-agent[bot]@users.noreply.github.com>

Author: savasp-agent[bot]

.editorconfig

@@ -414,3 +414,8 @@ dotnet_naming_style.s_camelcase.required_prefix = s_
 dotnet_naming_style.s_camelcase.required_suffix =
 dotnet_naming_style.s_camelcase.word_separator =
 dotnet_naming_style.s_camelcase.capitalization = camel_case
+
+# Retain the existing quality baseline while making the complete .NET security
+# analyzer set fail closed.
+[*.cs]
+dotnet_analyzer_diagnostic.category-Security.severity = error