run `go mod tidy` before building examples

[0xmohit]

Running make examples after cloning the repository gives the following error:

...
[100%] Built target whisper
gmake[3]: Leaving directory '/tmp/exp/whisper.cpp/bindings/go/build'
gmake[2]: Leaving directory '/tmp/exp/whisper.cpp/bindings/go/build'
gmake[1]: Leaving directory '/tmp/exp/whisper.cpp/bindings/go/build'
Build example go-model-download
Build example go-whisper
examples/go-whisper/process.go:11:2: missing go.sum entry for module providing pa
        go get github.com/ggerganov/whisper.cpp/bindings/go/examples/go-whisper
make: *** [Makefile:26: examples/go-whisper] Error 1

While there, also remove executable bit on files that don't need it.

[0xmohit]

cc: @djthorpe