Use 'python3' to access Python (TriBITSPub#610)

As per https://peps.python.org/pep-0394, it is best practice to not use
'python' in shebangs. Use the explicit `python3` entry point instead.

Signed-off-by: Samuel E. Browne <[email protected]>

common_tools/git/cherry-pick-commits.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 # @HEADER
 # ************************************************************************
 #

common_tools/git/commit-summary-over-periods.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 # @HEADER
 # ************************************************************************
 #

common_tools/git/hooks/server-side/get_recipients.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 
 import commands
 import os

common_tools/git/hooks/server-side/update_push_log.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 # @HEADER
 # ************************************************************************
 #

common_tools/test/hhmmss_math.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 #
 # This simple set of python functions makes it easy to do simple math with
 # times formatted as <hr>h<min>m<sec>s.  This makes it easier to analyze

common_tools/test/kill-pstree.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 # @HEADER
 # ************************************************************************
 #

refactoring/remove_std_tribits_includes.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 
 include_files_to_remove = [
   "AddSubdirectories",