all: run.{bash,bat,rc} sets GOPATH inconsistently [1.15 backport] #45239
Description
@dmitshur requested issue #45238 to be considered for backport to the next 1.15 minor release.
@gopherbot Please consider this for backport.
This should be a test-only fix, since releases use make.bash (all.bash is used only during release testing), and is needed to be able to run long tests for future 1.16 and 1.15 minor releases (issue #29252).