[bug]: clicking on chart in MAT doesn't correctly set probe_cc filters

[hellais]

Steps to reproduce:

• Filter by some country code in MAT (eg. https://explorer.ooni.org/chart/mat?probe_cc=PK&since=2024-10-01&until=2026-01-01&time_grain=week&axis_x=measurement_start_day&test_name=signal)
• Click on the chart bar and "view measurements"
• Notice how it doesn't correct apply the filter, but rather redirects to full country list