OBNARUZHENIE RASPADA $pi$° + $gamma$ $omega$°-MEZONOV, ROZHDENNYKH $pi$â»-MEZONAMI S IMPUL'SOM 9 GeV/c V $pi$â»-Xe VZAIMODEISTVIYAKH. (Detection of the $pi$° + $gamma$-Decay of $omega$°-Mesons Produced by $pi$â»-Mesons With the 9 GeV/c Momentum in $pi$â»-Xe Interactions).