fix: avoid `catch (...)` for expected `import numpy` failures (#3974)

* Replace import numpy catch (...) with catch (error_already_set)

* Add missing const (not sure how those got lost).

tests/test_numpy_array.cpp

@@ -162,7 +162,7 @@ static int data_i = 42;
 TEST_SUBMODULE(numpy_array, sm) {
     try {
         py::module_::import("numpy");
-    } catch (...) {
+    } catch (const py::error_already_set &) {
         return;
     }
 

tests/test_numpy_dtypes.cpp

@@ -301,7 +301,7 @@ struct B {};
 TEST_SUBMODULE(numpy_dtypes, m) {
     try {
         py::module_::import("numpy");
-    } catch (...) {
+    } catch (const py::error_already_set &) {
         return;
     }
 

tests/test_numpy_vectorize.cpp

@@ -22,7 +22,7 @@ double my_func(int x, float y, double z) {
 TEST_SUBMODULE(numpy_vectorize, m) {
     try {
         py::module_::import("numpy");
-    } catch (...) {
+    } catch (const py::error_already_set &) {
         return;
     }