testing: "=== PAUSE" lines do not change the test name for the next log line [1.15 backport]

[gopherbot]

@bcmills requested issue #40657 to be considered for backport to the next 1.15 minor release.

@gopherbot, please backport to 1.14 and 1.15: this is likely a regression from the original 1.14 release.

[gopherbot]

Change https://golang.org/cl/249097 mentions this issue: [release-branch.go1.15] testing: treat PAUSE lines as changing the active test name

[cagedmantis]

Approved as this is a critical issue without any workaround.

[gopherbot]

Closed by merging 0ffc567 to release-branch.go1.15.