Change warning text from "isn't supported" to "isn't recommended"

Updated NETSDK1234 warning text per feedback to be less severe.

Co-authored-by: marcpopMSFT <12663534+marcpopMSFT@users.noreply.github.com>

Author: Copilot

src/Tasks/Common/Resources/Strings.resx

@@ -1011,7 +1011,7 @@ You may need to build the project on another operating system or architecture, o
     <comment>{StrBegins="NETSDK1233: "}</comment>
   </data>
   <data name="CannotHaveSolutionLevelTargetFramework" xml:space="preserve">
-    <value>NETSDK1234: The "--framework" option isn't supported when building a solution. Specifying a solution-level framework results in all projects building for that framework, which can cause referenced projects to build multiple times and can lead to inconsistent builds.</value>
+    <value>NETSDK1234: The "--framework" option isn't recommended when building a solution. Specifying a solution-level framework results in all projects building for that framework, which can cause referenced projects to build multiple times and can lead to inconsistent builds.</value>
     <comment>{StrBegins="NETSDK1234: "}{Locked="--framework"}</comment>
   </data>
   <!-- The latest message added is CannotHaveSolutionLevelTargetFramework. Please update this value with each PR to catch parallel PRs both adding a new message -->