tests: show snapshot commit in testcurl

This disambiguates the source code being tested. The output format is
the same as when testing out of a git repo, but with no description and
a long hash.

Ref: #14363
Closes #14429

tests/testcurl.pl

@@ -77,7 +77,7 @@ use vars qw($name $email $desc $confopts $runtestopts $setupfile $mktarball
             $timestamp $notes);
 
 # version of this script
-$version='2023-03-28';
+$version='2024-08-07';
 $fixed=0;
 
 # Determine if we're running from git or a canned copy of curl,
@@ -484,6 +484,16 @@ if ($git) {
   else {
     logit "autoreconf -fi was successful (dummy message)";
   }
+
+} else {
+    # Show snapshot git commit when available
+    if (open (my $f, '<', "docs/tarball-commit.txt")) {
+      my $commit = <$f>;
+      chomp $commit;
+      logit "The most recent curl git commits:";
+      logit "  $commit";
+      close($f);
+    }
 }
 
 # Set timestamp to the one in curlver.h if this isn't a git test build.