fix pip syntax

Author: mikedh

build_dependencies/install_linux.sh

@@ -1,7 +1,7 @@
 # exit immediately on any failed step
 set -xe
 
-pip install cmake=3.31.6
+pip install cmake==3.31.6
 
 mkdir -p deps
 cd deps

build_dependencies/install_macos.sh

@@ -1,6 +1,6 @@
 # exit immediately on any failed step
 set -xe
-pip install cmake=3.31.6
+pip install cmake==3.31.6
 
 mkdir -p deps
 cd deps