[backport] chore: bump web_connectivity@v0.5 version to 0.5.5 (#945)

chore: web_connectivity v0.5.5

We're bumping the version number to reflect recent improvements in the
data format implemented in these pull requests:

- #942

- #943

- #944

Reference issue: ooni/probe#2238

internal/experiment/webconnectivity/measurer.go

@@ -36,7 +36,7 @@ func (m *Measurer) ExperimentName() string {
 
 // ExperimentVersion implements model.ExperimentMeasurer.
 func (m *Measurer) ExperimentVersion() string {
-	return "0.5.4"
+	return "0.5.5"
 }
 
 // Run implements model.ExperimentMeasurer.