ci: Set Codecov flags to categorize coverage

.github/workflows/server-mariadb-tests.yml

@@ -127,4 +127,5 @@ jobs:
           name: MariaDB
           fail_ci_if_error: true
           files: /home/runner/frappe-bench/sites/coverage.xml
-          verbose: true
+          verbose: true
+          flags: server

.github/workflows/server-postgres-tests.yml

@@ -131,3 +131,4 @@ jobs:
           fail_ci_if_error: true
           files: /home/runner/frappe-bench/sites/coverage.xml
           verbose: true
+          flags: server

.github/workflows/ui-tests.yml

@@ -154,3 +154,4 @@ jobs:
           fail_ci_if_error: true
           directory: /home/runner/frappe-bench/apps/frappe/.cypress-coverage/
           verbose: true
+          flags: ui-tests

codecov.yml

@@ -9,5 +9,15 @@ coverage:
         threshold: 0.5%
 
 comment:
-  layout: "diff"
+  layout: "diff, flags"
   require_changes: true
+
+flags:
+  server:
+    paths:
+      - ".*\.py"
+    carryforward: true
+  ui-tests:
+    paths:
+      - ".*\.js"
+    carryforward: true