Fix variable scope (#21)

It seems in julia 1.10, the variable needs to be declared outside of the
`try`/`if` block, otherwise it complains

```julia
ERROR: LoadError: UndefVarError: `format` not defined
```

src/w90/nnkp.jl

@@ -127,14 +127,11 @@ function read_nnkp(filename::AbstractString, ::Wannier90Toml)
 end
 
 function read_nnkp(filename::AbstractString)
+    format = Wannier90Text()
     try
         TOML.parsefile(filename)
     catch err
-        if err isa TOML.ParserError
-            format = Wannier90Text()
-        else
-            rethrow()
-        end
+        err isa TOML.ParserError || rethrow()
     else
         format = Wannier90Toml()
     end

src/w90/win.jl

@@ -316,14 +316,11 @@ function read_win(filename::AbstractString, ::Wannier90Toml; fix_inputs::Bool=tr
 end
 
 function read_win(filename::AbstractString; fix_inputs=true)
+    format = Wannier90Text()
     try
         TOML.parsefile(filename)
     catch err
-        if err isa TOML.ParserError
-            format = Wannier90Text()
-        else
-            rethrow()
-        end
+        err isa TOML.ParserError || rethrow()
     else
         format = Wannier90Toml()
     end