[ci] fix install_silx

Status Job ID Name Coverage
  Test
canceled #68433
test:python3.5-stretch-pyqt5_larch

passed #67758
test:python3.5-stretch-pyqt5_pymca

00:10:31

canceled #68434
test:python3.5-stretch-pyqt5_pymca_larch

passed #67761
test:test-est-tutorials_pymca

00:07:05

canceled #68395
test:python3.5-stretch-pyqt5_larch

00:14:13

canceled #67755
test:python3.5-stretch-pyqt5_larch

failed #67759
test:python3.5-stretch-pyqt5_larch

02:00:09

canceled #67754
test:python3.5-stretch-pyqt5_pymca

canceled #68396
test:python3.5-stretch-pyqt5_pymca_larch

00:14:13

failed #67760
test:python3.5-stretch-pyqt5_pymca_larch

01:56:31

canceled #67756
test:python3.5-stretch-pyqt5_pymca_larch

canceled #67757
test:test-est-tutorials_pymca