ci: explicitly call waf with python3

Python 2 may not be present in the CI images in the future,
but waf’s shebang line still uses its executable name.
Explicitly call the right major version of the interpreter.

ci/build-mingw64.sh

@@ -16,7 +16,7 @@ export RANLIB=$TARGET-ranlib
 export CFLAGS="-O2 -mtune=intel -g -ggdb -pipe -Wall --param=ssp-buffer-size=4 -mms-bitfields -fmessage-length=0 -D_FORTIFY_SOURCE=2 -fexceptions -fasynchronous-unwind-tables -fstack-protector-strong -fno-ident"
 export LDFLAGS="-Wl,--no-keep-memory -fstack-protector-strong"
 
-./waf configure \
+python3 ./waf configure \
     --enable-static-build \
     --enable-libmpv-shared \
     --enable-lua \
@@ -31,4 +31,4 @@ export LDFLAGS="-Wl,--no-keep-memory -fstack-protector-strong"
     --enable-shaderc \
     --enable-rubberband \
     --enable-lcms2
-./waf build --verbose
+python3 ./waf build --verbose

ci/build-tumbleweed.sh

@@ -1,7 +1,7 @@
 #!/bin/sh
 set -e
 
-./waf configure \
+python3 ./waf configure \
   --enable-cdda          \
   --enable-dvbin         \
   --enable-dvdnav        \
@@ -13,4 +13,4 @@ set -e
   --enable-shaderc       \
   --enable-vulkan        \
   --enable-zsh-comp
-./waf build --verbose
+python3 ./waf build --verbose