runtests: add -m=seconds to override test curl command timeout

To override the curl default of 5 minutes (300000 ms).

Sometimes a simple test data change can result in a stuck test, this
option makes it exit with an error early. Possible future use in CI
or fast machines to prevent a single test taking 5 minutes and failing
the whole job.

Example hangers:

tests/data/test65:
```diff
-<data1000 crlf="yes">
+<data1000 crlf="headers">
```

tests/data/tests993:
```diff
-%repeat[1000 x 95 328485%0d%0a]%</data>
+%repeat[1000 x 95 328485%0d%0a]%
+</data>
```

Closes #19319

tests/data/test1407

@@ -109,6 +109,7 @@ $_ = '' if /CURLOPT_HTTP_VERSION/
 $_ = '' if /CURLOPT_HTTP09_ALLOWED/
 $_ = '' if /CURLOPT_INTERLEAVEDATA/
 $_ = '' if /CURLOPT_SSLVERSION/
+$_ = '' if /CURLOPT_TIMEOUT_MS/
 </stripfile>
 </verify>
 </testcase>