tcl setup required on any Ubuntu, not just latest

Build failed because Tcl was not installed on Ubuntu. Since we're using the
"ubuntu-24.04" string for now, we need to match on a prefix instead of the exact
value.

.github/workflows/build.yml

@@ -53,7 +53,7 @@ jobs:
           dotnet-version: '6.0.X'
 
       - name: Setup tcl (ubuntu)
-        if: matrix.os == 'ubuntu-latest'
+        if: startsWith(matrix.os, 'ubuntu-')
         run: sudo apt-get update && sudo apt-get install tcl-dev
 
       - name: Setup tcl (macos-latest)