wasm: set EMSDK_PYTHON to Python installed in provisioning

Emscripten 4.0.7 requires Python +3.8, OpenSUSE does have Python 3.11
but its path is only set to PYTHON3_EXECUTABLE envvar defined in
08-pythondev.sh.

OpenSUSE 15.6 comes with Python 3.6.15 which the previous emscripten
3.1.70 used.

Change-Id: Ied63ace32b7fb252d124ad447bc56dba353ff403
Reviewed-by: Lorn Potter <lorn.potter@qt.io>
(cherry picked from commit 7471b6b6d2)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

coin/provisioning/common/unix/emsdk.sh

@@ -53,5 +53,6 @@ SetEnvVar "PATH" "\"\$PATH:${emscriptenPath}\""
 SetEnvVar "EMSCRIPTEN" "${emscriptenPath}"
 SetEnvVar "EMSDK" "${emsdkPath}"
 SetEnvVar "EMSDK_NODE" "${emsdkPath}${pathNodeExecutable}"
+SetEnvVar "EMSDK_PYTHON" "$PYTHON3_EXECUTABLE"
 
 echo "Emsdk = $version" >> ~/versions.txt

coin/provisioning/qtci-linux-openSUSE-15.6-x86_64/08-pythondev.sh

@@ -3,7 +3,7 @@
 
 # provides: python development libraries
 # version: provided by default Linux distribution repository
-# needed to build pyside
+# needed to build pyside and emsdk for WebAssembly
 
 set -ex