cmd/internal/buildid: close ELF file after reading note

Updates #26400

Change-Id: I1747d1f1018521cdfa4b3ed13412a944829967cf
Reviewed-on: https://go-review.googlesource.com/124235
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/cmd/internal/buildid/note.go

@@ -30,6 +30,7 @@ func ReadELFNote(filename, name string, typ int32) ([]byte, error) {
 	if err != nil {
 		return nil, err
 	}
+	defer f.Close()
 	for _, sect := range f.Sections {
 		if sect.Type != elf.SHT_NOTE {
 			continue