Use more specific override variable name for unit test regex

Task has the capability for a default template value to be specified, which may be overridden by an environment variable
set by the task user. The previous variable name chosen for this purpose was somewhat ambiguous.

Author: per1234

Taskfile.yml

@@ -72,8 +72,8 @@ tasks:
       - |
         go test \
           -short \
-          -run '{{default ".*" .TEST_REGEX}}' \
           {{default "-v" .GOFLAGS}} \
+          -run '{{default ".*" .GO_TEST_REGEX}}' \
           -coverprofile=coverage_unit.txt \
           {{default .DEFAULT_GO_PACKAGES .GO_PACKAGES}}