runtests: add options to set minimum number of tests, use them

To detect mistakes made in the runtests framework that reduce
the number of test runs. Before this patch it could go undetected with
a green CI.

The minimum thresholds will need light maintenance going forward (either
bumping them periodically, or adjust if some may fell below minimums for
justified reasons). We may also make minimums tighter or looser, or more
job-specific.

Latest number of test runs for each job can be seen at Test Clutch:
https://testclutch.curl.se/static/reports/feature-matrix.html

Also:
- GHA: set minimums.

Assisted-by: Dan Fandrich

Follow-up to f2a75a14dd
Follow-up to bb1391f943 #19510

Closes #19942

tests/globalconfig.pm

@@ -50,6 +50,7 @@ BEGIN {
         $LOCKDIR
         $LOGDIR
         $maxtime
+        $mintotal
         $memanalyze
         $MEMDUMP
         $perlcmd
@@ -104,6 +105,7 @@ our $CURLVERSION="";  # curl's reported version number
 our $CURLVERNUM="";   # curl's reported version number (without -DEV)
 our $randseed = 0;    # random number seed
 our $maxtime;         # curl command timeout override
+our $mintotal;        # minimum number of tests to run
 
 # paths
 our $pwd = getcwd();  # current working directory

tests/runtests.pl

@@ -2403,6 +2403,10 @@ while(@ARGV) {
         my ($num)=($1);
         $maxtime=$num;
     }
+    elsif($ARGV[0] =~ /--min=(\d+)/) {
+        my ($num)=($1);
+        $mintotal=$num;
+    }
     elsif($ARGV[0] eq "-n") {
         # no valgrind
         undef $valgrind;
@@ -2546,6 +2550,7 @@ Usage: runtests.pl [options] [test selection(s)]
   -L path  require an additional perl library file to replace certain functions
   -l       list all test case names/descriptions
   -m=[seconds] set timeout for curl commands in tests
+  --min=[count] minimum number of tests to run.
   -n       no valgrind
   --no-debuginfod disable the valgrind debuginfod functionality
   -o variable=value set internal variable to the specified value
@@ -3332,6 +3337,19 @@ else {
     }
 }
 
+if(!$mintotal && $ENV{"CURL_TEST_MIN"}) {
+    $mintotal = $ENV{"CURL_TEST_MIN"};
+}
+if($mintotal) {
+    if($total < $mintotal) {
+        logmsg "TESTFAIL: number of tests run was below the minimum of: $mintotal\n";
+        exit 1;
+    }
+    else {
+        logmsg "TESTDONE: minimum number of tests was met: $mintotal\n";
+    }
+}
+
 if(($total && (($ok+$ign) != $total)) || !$total || $unexpected) {
     exit 1;
 }