shorten 'go test -short' run time

Down from ~11s to ~7s, as we can skip some extra checks.

While at it, avoid duplicate 'go test' builds in test.txt.

testdata/scripts/basic.txt

@@ -28,6 +28,8 @@ cmp stderr main.stderr
 
 ! bingrep main$exe ${WORK@R} 'globalVar' 'globalFunc'
 
+[short] stop # checking that the build is reproducible is slow
+
 # Finally, check that the 'garble build' shortcut works, and produces the same
 # binary.
 cp main$exe main_old$exe

testdata/scripts/imports.txt

@@ -4,6 +4,8 @@ cmp stdout main.stdout
 
 ! bingrep main$exe 'ImportedVar' 'ImportedConst' 'ImportedFunc' 'ImportedType'
 
+[short] stop # checking that the build is reproducible is slow
+
 # Also check that the binary is reproducible when many imports are involved.
 cp main$exe main_old$exe
 rm main$exe

testdata/scripts/test.txt

@@ -1,13 +1,13 @@
 exec go test -v
 stdout 'PASS.*TestFoo'
 
-garble test -v
-stdout 'PASS.*TestFoo'
-
 garble test -c -vet=off
 bingrep bar.test$exe 'TestFoo'
 ! bingrep bar.test$exe 'ImportedVar'
 
+exec ./bar.test -test.v
+stdout 'PASS.*TestFoo'
+
 -- go.mod --
 module foo.com/bar
 -- bar.go --