Kotlin: bump default CI version to 1.7.20

A bunch of test expectations change because 7f531d8426 means that we now see (a) local variable declarations with source locations covering only their identifier, not the whole statement, and (b) more SYNTHETIC_OFFSET values for the parts of a destructuring assignment
or initialiser, which show up as file.kt:0:0:0:0 in DbLocation form.

java/kotlin-extractor/gradle.properties

@@ -1,5 +1,5 @@
 kotlin.code.style=official
-kotlinVersion=1.7.0
+kotlinVersion=1.7.21
 
 GROUP=com.github.codeql
 VERSION_NAME=0.0.1

java/kotlin-extractor/kotlin_plugin_versions.py

@@ -22,10 +22,10 @@ def version_string_to_tuple(version):
     return tuple([int(m.group(i)) for i in range(1, 4)] + [m.group(4)])
 
 # Version number used by CI. It needs to be one of the versions in many_versions.
-ci_version = '1.7.0'
+ci_version = '1.7.20'
 
 # Version numbers in the list need to be in semantically increasing order
-many_versions = [ '1.4.32', '1.5.0', '1.5.10', '1.5.20', '1.5.30', '1.6.0', '1.6.20', '1.7.0', '1.7.20-Beta' ]
+many_versions = [ '1.4.32', '1.5.0', '1.5.10', '1.5.20', '1.5.30', '1.6.0', '1.6.20', '1.7.0', '1.7.20' ]
 
 many_versions_tuples = [version_string_to_tuple(v) for v in many_versions]