github/workflows: remove some pip3 usages

When this was originally added, some OS package managers were slow and
behind the required meson version needed for mpv to build. Both opensuse
tumbleweed and freebsd now appear to carry meson 0.60.3 in their repos
so we no longer need to do the two-step process of installing pip3 and
then installing meson via pip. Instead, just use the OS package manager
version.

.github/workflows/build.yml

@@ -126,10 +126,7 @@ jobs:
       - name: Install dependencies
         run: |
           ./bootstrap.py
-          # TODO: switch back to zypper when OpenSuse updates Meson
-          # zypper -n install meson
-          zypper -n install python3-pip
-          pip install --no-input meson ninja
+          zypper -n install meson
 
       - name: Build with meson
         run: |
@@ -166,6 +163,7 @@ jobs:
                 libplacebo \
                 libxkbcommon \
                 luajit \
+                meson \
                 openal-soft \
                 pkgconf \
                 python3 \
@@ -190,8 +188,5 @@ jobs:
                 uchardet \
                 v4l_compat \
                 #
-            # Meson from pkg is too old
-            python3 -m ensurepip
-            pip3 install --no-input meson ninja
         run: |
           ./ci/build-freebsd.sh