Fix tabs

Author: adegeo

docs/core/install/linux-ubuntu-install.md

@@ -44,6 +44,10 @@ When an [Ubuntu version](https://wiki.ubuntu.com/Releases) falls out of support,
 
 [!INCLUDE [linux-apt-install-80](includes/linux-install-80-apt.md)]
 
+# [.NET 6](#tab/dotnet6)
+
+Not available.
+
 ---
 
 ## Dependencies
@@ -86,6 +90,10 @@ The following versions of .NET are supported or available for Ubuntu 24.04:
 
 When an [Ubuntu version](https://wiki.ubuntu.com/Releases) falls out of support, .NET is no longer supported with that version.
 
+# [.NET 9](#tab/dotnet9)
+
+Not available.
+
 # [.NET 8](#tab/dotnet8)
 
 [!INCLUDE [linux-apt-install-80](includes/linux-install-80-apt.md)]
@@ -141,6 +149,10 @@ The following versions of .NET are supported or available for Ubuntu 22.04:
 
 When an [Ubuntu version](https://wiki.ubuntu.com/Releases) falls out of support, .NET is no longer supported with that version.
 
+# [.NET 9](#tab/dotnet9)
+
+Not available.
+
 # [.NET 8](#tab/dotnet8)
 
 [!INCLUDE [linux-apt-install-80](includes/linux-install-80-apt.md)]
@@ -202,6 +214,10 @@ sudo dpkg -i packages-microsoft-prod.deb
 rm packages-microsoft-prod.deb
 ```
 
+# [.NET 9](#tab/dotnet9)
+
+Not available.
+
 # [.NET 8](#tab/dotnet8)
 
 [!INCLUDE [linux-apt-install-80](includes/linux-install-80-apt.md)]
@@ -281,6 +297,10 @@ The following versions of .NET were supported or available for Ubuntu 23.10:
 
 When an [Ubuntu version](https://wiki.ubuntu.com/Releases) falls out of support, .NET is no longer supported with that version.
 
+# [.NET 9](#tab/dotnet9)
+
+Not available.
+
 # [.NET 8](#tab/dotnet8)
 
 [!INCLUDE [linux-apt-install-80](includes/linux-install-80-apt.md)]
@@ -330,6 +350,10 @@ The following versions of .NET were supported or available for Ubuntu 23.04:
 
 [!INCLUDE [linux-ubuntu-feed-sdk-note](includes/linux-ubuntu-feed-sdk-note.md)]
 
+# [.NET 9](#tab/dotnet9)
+
+Not available.
+
 # [.NET 8](#tab/dotnet8)
 
 [!INCLUDE [linux-ubuntu-80-ms](includes/linux-ubuntu-80-ms.md)]
@@ -381,6 +405,10 @@ The following versions of .NET are supported or available for Ubuntu 22.10:
 
 [!INCLUDE [linux-ubuntu-feed-sdk-note](includes/linux-ubuntu-feed-sdk-note.md)]
 
+# [.NET 9](#tab/dotnet9)
+
+Not available.
+
 # [.NET 8](#tab/dotnet8)
 
 .NET 8 isn't supported on Ubuntu 22.10.