Revert "use Qt 5.15.3"

This reverts commit 5a8eb1e7aa3f9dc224727e4dc157b5ee54d975c1.

.github/workflows/ci-linux.yml

@@ -45,12 +45,12 @@ jobs:
         uses: actions/cache@v1  # not v2!
         with:
           path: ../Qt
-          key: ${{ runner.os }}-QtCache-5.15-2
+          key: ${{ runner.os }}-QtCache-5.15-1
 
       - name: Install Qt
         uses: jurplel/install-qt-action@v2
         with:
-          version: 5.15.3
+          version: 5.15.2
           target: desktop
           modules: qtwebengine
           tools: tools_openssl_x64,1.1.1-4,qt.tools.openssl.gcc_64

.github/workflows/ci-macos.yml

@@ -44,12 +44,12 @@ jobs:
         uses: actions/cache@v1  # not v2!
         with:
           path: ../Qt
-          key: ${{ runner.os }}-QtCache-5.15-2
+          key: ${{ runner.os }}-QtCache-5.15-1
 
       - name: Install Qt
         uses: jurplel/install-qt-action@v2
         with:
-          version: 5.15.3
+          version: 5.15.2
           target: desktop
           modules: qtwebengine
           cached: ${{ steps.cache-qt.outputs.cache-hit }}

.github/workflows/ci-win.yml

@@ -50,12 +50,12 @@ jobs:
         uses: actions/cache@v1  # not v2!
         with:
           path: ../Qt
-          key: ${{ runner.os }}-${{matrix.config.arch}}-QtCache-5.15-2
+          key: ${{ runner.os }}-${{matrix.config.arch}}-QtCache-5.15-1
 
       - name: Install Qt
         uses: jurplel/install-qt-action@v2
         with:
-          version: 5.15.3
+          version: 5.15.2
           target: desktop
           arch: ${{matrix.config.arch}}
           modules: qtwebengine

src/src.pro

@@ -1,6 +1,6 @@
 lessThan(QT_MAJOR_VERSION, 5): error("requires Qt 5 and above")
 
-equals(QT_MAJOR_VERSION, 5):lessThan(QT_MINOR_VERSION, 15): error("requires Qt 5.15 and above")
+equals(QT_MAJOR_VERSION, 5):lessThan(QT_MINOR_VERSION, 12): error("requires Qt 5.12 and above")
 
 QT += core gui widgets webenginewidgets webchannel network svg printsupport
 QT += sql