test-bot pathname: use Utils.popen_read instead of backticks

Closes Homebrew/homebrew#37418.

Signed-off-by: Xu Cheng <xucheng@me.com>

Library/Homebrew/cmd/test-bot.rb

@@ -365,12 +365,12 @@ module Homebrew
       end
 
       test "brew", "uses", canonical_formula_name
-      dependencies = `brew deps #{canonical_formula_name}`.split("\n")
-      dependencies -= `brew list`.split("\n")
+      dependencies = Utils.popen_read("brew", "deps", canonical_formula_name).split("\n")
+      dependencies -= Utils.popen_read("brew", "list").split("\n")
       unchanged_dependencies = dependencies - @formulae
       changed_dependences = dependencies - unchanged_dependencies
 
-      dependents = `brew uses --skip-build --skip-optional #{canonical_formula_name}`.split("\n")
+      dependents = Utils.popen_read("brew", "uses", "--skip-build", "--skip-optional", canonical_formula_name).split("\n")
       dependents -= @formulae
       dependents = dependents.map {|d| Formulary.factory(d)}
 
@@ -573,7 +573,7 @@ module Homebrew
       non_dependencies = []
 
       @formulae.each do |formula|
-        formula_dependencies = `brew deps #{formula}`.split("\n")
+        formula_dependencies = Utils.popen_read("brew", "deps", formula).split("\n")
         unchanged_dependencies = formula_dependencies - @formulae
         changed_dependences = formula_dependencies - unchanged_dependencies
         changed_dependences.each do |changed_formula|

Library/Homebrew/extend/pathname.rb

@@ -413,10 +413,11 @@ class Pathname
   end
 
   def abv
-    out=''
-    n=`find #{to_s} -type f ! -name .DS_Store | wc -l`.to_i
+    out = ""
+    n = Utils.popen_read("find", expand_path.to_s, "-type", "f", "!", "-name", ".DS_Store").split("\n").size
     out << "#{n} files, " if n > 1
-    out << `/usr/bin/du -hs #{to_s} | cut -d"\t" -f1`.strip
+    out << Utils.popen_read("/usr/bin/du", "-hs", expand_path.to_s).split("\t")[0]
+    out
   end
 
   # We redefine these private methods in order to add the /o modifier to