Fix the security update version check message for PyPy (#1040)

Previously if an app was using an older version of PyPy, the buildpack
would show a confusing "Could not find that version" message (even
though the version was found), when it really meant to warn about there
being a newer release available.

It looks like the version check messages were perhaps copied and pasted
from something else, but the message wording not updated at the time.

I've also added tests since there were none for this feature.

Fixes #1004.
Closes @W-7918745@.

test/fixtures/pypy2_7/runtime.txt

@@ -1 +1 @@
-pypy2.7-7.2.0
+pypy2.7-7.3.1

test/fixtures/pypy2_7_warn/runtime.txt

@@ -0,0 +1 @@
+pypy2.7-7.2.0

test/fixtures/pypy3_6/runtime.txt

@@ -1 +1 @@
-pypy3.6-7.2.0
+pypy3.6-7.3.1

test/fixtures/pypy3_6_warn/runtime.txt

@@ -0,0 +1 @@
+pypy3.6-7.2.0

test/run-versions

@@ -197,24 +197,42 @@ testPython3_8_fail() {
 
 testPypy3_6() {
   compile "pypy3_6"
+  assertCaptured "Installing pypy"
+  assertNotCaptured "security update"
+  assertCaptured "$PYPY_36"
+  assertCaptured "Installing pip 20.1.1, setuptools 47.1.1 and wheel 0.34.2"
+  assertCapturedSuccess
+}
+
+testPypy3_6_warn() {
+  compile "pypy3_6_warn"
   if [[ $STACK = "cedar-14" ]]; then
     assertCapturedError
   else
     assertCaptured "Installing pypy"
+    assertCaptured "security update!"
     assertCaptured "$PYPY_36"
-    assertCaptured "Installing pip 20.1.1, setuptools 47.1.1 and wheel 0.34.2"
     assertCapturedSuccess
   fi
 }
 
 testPypy2_7() {
   compile "pypy2_7"
+  assertCaptured "Installing pypy"
+  assertNotCaptured "security update"
+  assertCaptured "$PYPY_27"
+  assertCaptured "Installing pip 20.1.1, setuptools 44.1.1 and wheel 0.34.2"
+  assertCapturedSuccess
+}
+
+testPypy2_7_warn() {
+  compile "pypy2_7_warn"
   if [[ $STACK = "cedar-14" ]]; then
     assertCapturedError
   else
     assertCaptured "Installing pypy"
+    assertCaptured "security update!"
     assertCaptured "$PYPY_27"
-    assertCaptured "Installing pip 20.1.1, setuptools 44.1.1 and wheel 0.34.2"
     assertCapturedSuccess
   fi
 }