log-cf-common: let mktime determine proper tz

In some timezones, LogCustomFormatTest01 was failing as we were
specifying the wrong setting for is_dst. Instead set it to -1 so mktime
can make the decision based on the environment. Appears to fix this test
for "Brazil/East" in the summer.

Add GitHub CI tests to test this specific test with a few different
timezones.

.github/workflows/builds.yml

@@ -1409,6 +1409,10 @@ jobs:
       - run: make install-headers
       - run: make install-library
 
+      - run: TZ="UTC" ./src/suricata -u -U LogCustomFormatTest01
+      - run: TZ="Brazil/East" ./src/suricata -u -U LogCustomFormatTest01
+      - run: TZ="Saskatchewan/Regina" ./src/suricata -u -U LogCustomFormatTest01
+
   ubuntu-24-04-rust-vars:
     name: Ubuntu 24.04 (RUSTC+CARGO vars)
     runs-on: ubuntu-latest

src/log-cf-common.c

@@ -245,7 +245,7 @@ static int LogCustomFormatTest01(void)
     tm.tm_year = 114;
     tm.tm_wday = 1;
     tm.tm_yday = 13;
-    tm.tm_isdst = 0;
+    tm.tm_isdst = -1;
     SCTime_t ts = SCTIME_FROM_SECS(mktime(&tm));
 
     MemBuffer *buffer = MemBufferCreateNew(62);