Update index.yml (Typo "Postgres version"→"PostgreSQL version")

https://docs.microsoft.com/en-us/azure/postgresql/flexible-server/
https://github.com/MicrosoftDocs/azure-docs/blob/main/articles/postgresql/flexible-server/index.yml
related #90044
#PingMSFTDocs

Author: hyoshioka0128

articles/postgresql/flexible-server/index.yml

@@ -51,7 +51,7 @@ landingContent:
             url: concepts-networking.md
           - text: Firewall Rules
             url: concepts-firewall-rules.md
-          - text: Postgres versions
+          - text: PostgreSQL versions
             url: concepts-supported-versions.md
           - text: Extensions
             url: concepts-extensions.md