IMPALA-13279: Upgrade gcovr to 7.2

In some environments, the code coverage report is empty even
though the tests ran successfully and gcno/gcda files are
written properly.

This upgrades to gcovr 7.2, which does not show the same
problem. gcovr 7.2 requires Python 3.8, so this switches to use
Python 3.8 from the toolchain and installs gcovr in the Python 3
virtualenv.

gcovr 7.2 outputs logging to stderr, so this also modifies
bin/coverage_helper.sh to redirect stderr to stdout.

Testing:
 - Verified that this can generate a report locally and on
   the affected environment

Change-Id: I5b1aaa92c65f54149a3e7230cbe56d5286f1051a
Reviewed-on: http://gerrit.cloudera.org:8080/21647
Reviewed-by: Michael Smith <michael.smith@cloudera.com>
Tested-by: Impala Public Jenkins <impala-public-jenkins@cloudera.com>

infra/python/deps/py3-requirements.txt

@@ -30,3 +30,13 @@ pylint == 2.10.2
   platformdirs == 2.4.1
   typing-extensions == 3.10.0.2
 k5test==0.10.3
+gcovr == 7.2
+  Jinja2 == 3.1.4
+    flit-core == 3.9.0
+  lxml == 5.2.2
+    Cython == 3.0.10
+  colorlog == 6.8.2
+  Pygments == 2.13.0
+    MarkupSafe == 2.1.5
+  tomli == 2.0.1
+    packaging == 24.1

infra/python/deps/requirements.txt

@@ -23,10 +23,6 @@
 allpairspy == 2.5.0
 argparse == 1.4.0
 future == 0.18.3
-gcovr == 4.2
-  Jinja2 == 2.11.3
-    MarkupSafe == 1.1.1
-  lxml == 4.9.1
 hdfs == 2.0.2
   docopt == 0.6.2
   execnet == 1.4.0