ci: fix directory existence racing in parallel test execution

meson tests sharing a binary (and deviating in their env/args) will
produce temporary logs to the same directory, which is assumed to exist
only for the duration of a single test. This is problematic when running
tests in parallel, as one test may remove the directory before the
other(s) finish, causing a test flake.

This appends the each test's pid to the output directory to enforce
uniqueness and avoid the race.

Signed-off-by: Ryan Neph <ryanneph@google.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/20779>

.gitlab-ci/meson/time-strace.sh

@@ -1,7 +1,7 @@
 #!/bin/sh
 
 if [ "x$STRACEDIR" = "x" ]; then
-    STRACEDIR=meson-logs/strace/$(for i in $@; do basename -z -- $i; echo -n _; done)
+    STRACEDIR=meson-logs/strace/$(for i in $@; do basename -z -- $i; echo -n _; done).$$
 fi
 
 mkdir -p $STRACEDIR