fix: check if external symbol before checking from same scope.

[arteevraina]

• [x] Resolves compilation failure for workaround mentioned here https://github.com/lcompilers/lpython/issues/2428#issuecomment-1817343501.
• [x] When the class is imported from another module as an ExternalSymbol, it should omit the same scope check in ASR Verify.

[certik]

I thought the ExternalSymbol should still be part of the current symbol table. I will need to investigate this.

Also let's add a test that now works.