GitHub actions: update Qt to 6.7.3 on macOS

In order to work around PCRE bug.

No updating on Windows since qwindowsvistastyle plugin
is cannot be found and requires further investigation.

Task-number: QBS-1799
Change-Id: Ic08ee88391a8c21a75a7c2277aa3eb5f9ad769b8

.github/workflows/main.yml

@@ -204,6 +204,7 @@ jobs:
       uses: ./.github/actions/download-qt
       with:
         toolchain: clang_64
+        version: 6.7.3
     - name: Install Qt Creator
       uses: ./.github/actions/download-qtc
     - name: Setup Qbs

tests/benchmarker/benchmarker.qbs

@@ -3,6 +3,7 @@ QtApplication {
     type: "application"
     consoleApplication: true
     cpp.cxxLanguageVersion: "c++20"
+    cpp.minimumMacosVersion: "11.0"
     condition: Qt.concurrent.present
     Depends { name: "qbsbuildconfig" }
     Depends {

tests/clang-format-test/clang-format-test.qbs

@@ -1,5 +1,7 @@
 QtApplication {
     Depends { name: "Qt.core" }
     files: "clang-format.cpp"
+    cpp.cxxLanguageVersion: "c++20"
+    cpp.minimumMacosVersion: "11.0"
     cpp.warningLevel: "none"
 }

tests/fuzzy-test/fuzzy-test.qbs

@@ -4,6 +4,7 @@ QtApplication {
     consoleApplication: true
     Depends { name: "qbsbuildconfig" }
     cpp.cxxLanguageVersion: "c++20"
+    cpp.minimumMacosVersion: "11.0"
     files: [
         "commandlineparser.cpp",
         "commandlineparser.h",