Stabilize r03940.vtc

I do not understand how to avoid the child panicking while it is being
killed for timeout. And removing the AZ() for this case only is not
a good idea.

***  v1    debug|Error: Child (36277) not dying (waitpid = 0), killing
***  v1    debug|Child (36277) died signal=6
***  v1    debug|Error: Child (36277) Panic at: Mon, 03 Jul 2023 15:18:50 GMT
***  v1    debug|Assert error in CLI_Run(), cache/cache_cli.c line 102:
***  v1    debug|  Condition((VCLI_WriteResult(heritage.cli_out, CLIS_OK, \"Ready\")) == 0) not true.

bin/varnishtest/tests/r03940.vtc

@@ -18,8 +18,9 @@ process p1 { varnishd \
 	-pstartup_timeout=3s -pcli_timeout=2s \
 	-n ${tmpdir}/p1 -a :0 -b none 2>&1
 } -expect-exit 0x2 -run
-process p1 -expect-text 0 0 \
-	"Child failed on launch within startup_timeout=3.00s"
+# expect-text does not work if a panic info pushes the
+# error out of the emulated terminal's view.
+shell {grep -q "Child failed on launch within startup_timeout=3.00s" ${p1_err}}
 
 ####
 # cli_timeout used, delay in stevedore open
@@ -39,7 +40,5 @@ process p2 { varnishd \
 	-n ${tmpdir}/p2 -a :0 -b none
 } -expect-exit 0x2 -run
 
-# expect-text does not work here because the panic info pushes the
-# error out of the emulated terminal's view.
-# And I do not want to rely on any x lines to be enough
+# see explanation of previous shell grep
 shell {grep -q "launch within cli_timeout=3.00s (tip: set startup_" ${p2_err}}