Update develop_approvaltests_fetch_content to test latest versions of…

… most dependencies

As this project has CI builds run every week, this should allow me to detect
earlier any breakages in ApprovalTests.cpp code due to dependencies updating.

For the value of this, see
approvals/ApprovalTests.cpp#168

Notes:
* Catch2 uses v2.x, as we don't yet support v3
* Boost uses 1.72.0 - see #1 for why.

develop_approvaltests_fetch_content/CMakeLists.txt

@@ -30,27 +30,27 @@ set(BoostVersion
 # Tested with versions in range: v2.3.0 ... v2.13.3
 # Does not work with devel, and v3 releases
 set(Catch2Version
-        "v2.13.3")
+        "v2.x")
 
 # Tested with versions in range: v4.0
 set(CppUTestVersion
-        "v4.0")
+        "master")
 
 # Tested with versions in range: 2.3.4 ... 2.4.1
 set(DocTestVersion
-        "2.4.1")
+        "master")
 
 # Tested with versions in range: 6.0.0 ... 7.1.2
 set(FmtVersion
-        "7.1.2")
+        "master")
 
 # Tested with versions in range: release-1.8.0 ... release-1.10.0
 set(GoogleTestVersion
-        "release-1.10.0")
+        "master")
 
 # Tested with versions in range: 1.1.7 ... 1.1.8
 set(UtVersion
-        "v1.1.8")
+        "master")
 
 # -------------------------------------------------------------------
 # boost