Update CODEOWNERS paths: fix invalid paths

- Azure/azure-sdk-tools#5088

and enabling stricter validation:
- Azure/azure-sdk-tools#4859

this PR:
- fixes invalid paths, to match rules explained [here](https://github.com/Azure/azure-sdk/blob/main/docs/policies/opensource.md#codeowners);
- removes `/**/tests.yml` and `/**/ci.yml`, to avoid all build failure notifications being routed to it once we enable the new regex-based, wildcard-supporting `CODEOWNERS` matcher, per: Azure/azure-sdk-tools#5088 (comment)

Once this PR is merged, I will enable the new `CODEOWNERS` matcher, similar to how it was done for `net` repo by these two PRs:
- Azure/azure-sdk-tools#5241
- Azure/azure-sdk-tools#5240

.github/CODEOWNERS

@@ -1,6 +1,14 @@
 # Instructions for CODEOWNERS file format and automatic build failure notifications:
 # https://github.com/Azure/azure-sdk/blob/main/docs/policies/opensource.md#codeowners
 
+################
+# Orphaned paths
+################
+# As of 2/9/2023 these paths have no owners:
+
+# /**
+# /AzureSDK.xcworkspace/
+
 ################
 # Automation
 ################
@@ -39,4 +47,3 @@
 # Eng Sys
 ###########
 /eng/                                               @benbp @weshaggard
-/**/ci.yml                                          @benbp